Airone Speedometer drive

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Barry Wilson

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Nov 4, 2018, 6:40:19 AM11/4/18
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Does anyone have details of the telescopic drive unit so that I can make one ? e.g.  close up pictures/dimensions/etc would be brilliant. I have the hub gearbox fitted so only need the tubular section details.

Any help would be appreciated.

I don't know if any owners of Airone's would be interested in sets of the original material cork rear damper discs, ( not composite copies) they are just under 3mm thick. I have made the tooling to produce them and tested on my Airone and they work very well. About £19 a set plus postage, which should be very little due to the weight/size.  A set is 12 pieces, eight large ones and four small ones for the ends.

My Airone had mainly hardboard ones which were in poor condition hence the tooling. Will take some pictures if there is any interest.

I am not a dealer/shop/sellar etc. I just thought it might help other restorers, if not, no worries.

Dont forget the speedo drive info please.

Regards

Barry

Dirk Van Ussel

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Nov 7, 2018, 4:05:04 AM11/7/18
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Op zondag 4 november 2018 12:40:19 UTC+1 schreef Barry Wilson:
Does anyone have details of the telescopic drive unit so that I can make one ? e.g.  close up pictures/dimensions/etc would be brilliant. I have the hub gearbox fitted so only need the tubular section details.

Any help would be appreciated.

The telescopic unit appears every now and then on Ebay. I think I paid mine some 136 € plus 5 for the clamps. For that price I wouldn't start making one...
Dirk 

Barry Wilson

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Nov 8, 2018, 9:59:07 AM11/8/18
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Thanks Dirk, however I have an extensive workshop and am a precsion engineer and I would still need a speedo and cable it totals about £500.  Its only a shaft and a tubular outer with bushes/bearings, material costs zero as I have lots of stock materials and labour zero as I am retired. I could be accused of having nothing better to do and they would be quite right.

Take care.

Barry.

Barry Wilson

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Nov 8, 2018, 10:00:19 AM11/8/18
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Dirk Van Ussel

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Nov 8, 2018, 1:01:33 PM11/8/18
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Hi Barry,

Main tube is 180 mm lo,g,18 mm diameter. Extension tube is 140 mm long, 7 mm diameter
Dirk 
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SED Sci

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Nov 8, 2018, 10:54:31 PM11/8/18
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Nice photos and description.  Go Barry!

Barry Wilson

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Nov 9, 2018, 9:43:37 AM11/9/18
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Thats brillant Dirk, I will have a go over winter and keep you posted with progress.
Many , Many, thanks..

Barry

Barry Wilson

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Nov 9, 2018, 9:52:08 AM11/9/18
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If I can fathom out the connection to the gearbox I will be well on the way.  Thanks for the encouragement.  Barry

guzz...@aol.com

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Nov 9, 2018, 11:25:18 AM11/9/18
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not sure which photos you have ,,,,,,,, 

Tim


-----Original Message-----
From: Barry Wilson <mrsh...@gmail.com>
To: Guzzi Singles <guzzi-...@googlegroups.com>
Sent: Fri, Nov 9, 2018 8:43 am
Subject: [guzzi-singles] Re: Airone Speedometer drive

Thats brillant Dirk, I will have a go over winter and keep you posted with progress.
Many , Many, thanks..

Barry

On Thursday, November 8, 2018 at 6:01:33 PM UTC, Dirk Van Ussel wrote:

Hi Barry,

Main tube is 180 mm lo,g,18 mm diameter. Extension tube is 140 mm long, 7 mm diameter
Dirk 
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Barry Wilson

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Nov 11, 2018, 10:42:01 AM11/11/18
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Hi Tim, I have four pictures of the ends protruding from the outer tube from Dirk, however your pic gives me a good idea of scale.  The gearbox output is a slotted shaft which is also threaded so I assume the end like a ball with the pin through it fits into that.  I have to also assume that the inner shaft rotates in bushes and slides into/over ? the lower shaft, which must must be splined or a single keyway/slot with the usual square reccess at the top for the bowden cable to fit into. If I can't get "real" details I will have to design my own version which may or may not be more complicated than Mr Guzzi's. I could do with a sample to borrow to copy but can appreciate the logistics of that plus how rare they are.

there is no hurry as the Airone won't be going anywhere until the spring, I am also fighting with the wiring, it all seemed to work and the dynamo charged the battery but after leaving the bike for two days the battery was flat. It seems to be draining to earth but I am struggling to find where .  Anyway thats what winters are for...........

Be good, or not !

Gordon de la Mare

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Nov 11, 2018, 11:18:03 AM11/11/18
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Did you leave the key in the headlight? 

Barry Wilson

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Nov 11, 2018, 11:35:45 AM11/11/18
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Hi Gordon, No I didn't,  I have removed each bulb and fuse in turn and the meter still shows a drain of about 0.5 volts. I even tried removing both wires from the dynamo, no difference.  I was using a standard muli-meter set on DC volts, however a mate suggested setting it on " current " instead, I did and it shows zero drain at any level of setting.  I intend putting it all back together e.g.  bulbs/switches etc in place and leaving it overnight to see if the battery voltage drops. It is a new battery which if not on the bike loses nothing in months.  How do you find a competent auto-electrician who worked on these 60 years ago ?  I will keep trying, all suggestions welcome.

guzz...@aol.com

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Nov 11, 2018, 11:39:05 AM11/11/18
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Barry,,,,,,, I don't own those parts pictured anymore,,,,,, one of our forum members does. I never did take the tube apart to look inside. The lower shaft had a slot in it for maybe a cotter pin connection by gear box ?  Why not just have a cable made and go direct from gauge to gear box and save some headaches. Function over period correctness ……...

Gordon de la Mare

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Nov 11, 2018, 11:47:57 AM11/11/18
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If you have any spray electrical contact cleaner then give a blast around the switch in the headlight in case the contact points are sticking and also make sure that the key is switched to the off (middle) position before removing it.  Sometimes the switchgear gets so worn that you can remove the key when it isn't in the off position and you get leakage.


Barry Wilson

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Nov 11, 2018, 11:53:09 AM11/11/18
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Its quiute simple Tim, It bugs me everytime I see it,  I think masochist comes to mind. it not as if its ever going to break any speed limits is it ?  I am sure the skin on the rice pudding is quite safe.  Thanks mate.

Barry Wilson

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Nov 11, 2018, 12:02:50 PM11/11/18
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I even bent back the tags and stripped the switch, cleaned the contacts and checked all soldered connections, they are all fine, I am pretty sure that the loom is not original as it contains three purple wires which come from the rear light loom right up to the eadlight, they are cut off at both ends.This in addition to the two rear/stop wires. It came to me with the bike stripped and the loom/regulator/headlight all connected to gether, All I have done is swap the seperate regulator for the modern solid state one inside the dynamo case. I am tempted to order a new loom from Italy but cannot be sure that is the answer either. I have now connected the battery and will check the 6.52 volts tomorrow evening for drainage.

Barry Wilson

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Nov 11, 2018, 12:05:59 PM11/11/18
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Hi Dirk, can you tell me if there is a slot up the length of the 7mm shaft which might drive the telescopic upper section ? 

On Thursday, November 8, 2018 at 6:01:33 PM UTC, Dirk Van Ussel wrote:

Gordon de la Mare

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Nov 11, 2018, 12:25:28 PM11/11/18
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I like this bit "All I have done is swap the separate regulator for the modern solid state one inside the dynamo case"

It should make no difference if the key is out and it is wired correctly.

I presume you've verified the wiring on page 102?

guzz...@aol.com

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Nov 11, 2018, 1:31:54 PM11/11/18
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a bicycle speedo works just fine as well ……….. I use one on my super alce :>)

Tim


-----Original Message-----
From: Barry Wilson <mrsh...@gmail.com>
To: Guzzi Singles <guzzi-...@googlegroups.com>
Sent: Sun, Nov 11, 2018 10:53 am
Subject: Re: [guzzi-singles] Re: Airone Speedometer drive

Its quiute simple Tim, It bugs me everytime I see it,  I think masochist comes to mind. it not as if its ever going to break any speed limits is it ?  I am sure the skin on the rice pudding is quite safe.  Thanks mate.

On Sunday, November 11, 2018 at 4:39:05 PM UTC, Tim wrote:
Barry,,,,,,, I don't own those parts pictured anymore,,,,,, one of our forum members does. I never did take the tube apart to look inside. The lower shaft had a slot in it for maybe a cotter pin connection by gear box ?  Why not just have a cable made and go direct from gauge to gear box and save some headaches. Function over period correctness ……...

Tim


-----Original Message-----
From: Barry Wilson <mrsh...@gmail.com>
To: Guzzi Singles <guzzi-...@googlegroups. com>
Sent: Sun, Nov 11, 2018 9:42 am

Andrew Nahum

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Nov 11, 2018, 4:26:49 PM11/11/18
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Have you tried a wireless bike speedo?  I have not dared because I guessed the magneto sparks would upset if. If they do work someone please let me know. 

But I have used the wire connected kind on a couple of bikes and they are great. I aim to get near the right speed by programming in the tyre circumference which I measure with a dressmaker’s tape measure. The programming is usually a pain in the neck. 

Then I check the speed it shows by gaffer-taping on a GPS satnav and tune the cycle speedo by adjusting the inputted frontvwheel circumference. 

In London we have 20 mph zones with camera enforcement so it’s nice to know what you are doing even on a Guzzino. But my old Airone, which Mike Peavey now has, would, I felt sure, pull a good 70 mph given time and a clear road and I believe it can look at 75 and so fine to get you busted - less of that  ‘skin off a rice pudding’ talk !! !

My current ‘47 Airone Sport did not seem to want to go past 62 mph at first which puzzled me because it feels crisp and good. But I have the feeling it’s getting faster as I keep riding it with a handful of throttle. 

Andrew 

PS
However the period speedometer with that telescoping drive is a much nicer thing than the bicycle digits instrument. Respect for re-engineering one!

guzz...@aol.com

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Nov 11, 2018, 6:45:46 PM11/11/18
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I use the wired speedo on the SA ……… and on a Norton commando 

Tim

SED Sci

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Nov 11, 2018, 9:30:37 PM11/11/18
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Both cables and telescoping drives were used on Falcones.  Cable for sports I think.  Both versions are in the parts books. 

richard...@hotmail.co.uk

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Nov 12, 2018, 3:19:41 AM11/12/18
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Hi Barry,
Where do you live? If you are within 100 miles of me I will be happy to bring the complete speedo drive from my Arone for you to inspect. I’m not keen to hand it over to the post for obvious reasons.
I live on the edge of north London.

Richard

Barry Wilson

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Nov 12, 2018, 12:48:41 PM11/12/18
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Hi Gordon, my Italian is poor to none existant so the manual which I have ( the same as this one ) doesn't help with  the problems pages.  I am sure the loom is wrong and none of the colours match, or if they do it looks like a coincidence. I also have an extra fuse panel mounted at the top of the connections strip along the bottom of the headlight shell.  As it was all in bits the wiring etc could be Falcone etc but it doesn't match the circuit for any single around that era.  Were it not for the fact that the soldered connections are clearly original 50's I would have suspected a home made loom but it isn't.

As you can see electrics are not my forte, and sods law says everytime I build a 50's Guzzi, ( this is the third, 2 Lodola's before ) the electrics are rubbish and messed about with.  never mind I can't thank you guys enough for the help and advice you offer.   I will get there.  Your comment about swapping the regulator is rather apt as no-one seems to be able to explain why my dynamo ( why mine ??? ) has TWO field coils, hence two pairs of wires coming through to the brushes/regulator.  I had no help from the seller of the solid state regulator as he wasn't familiar with Magnetti Marreli stuff, he suggested just connecting them in parallel and it does produce just over 7 volts so something must be right.  I think that just about expends all my knowledge of electrics, I hide behind being a precision engineer not a sparky.

The voltage didn't drop last night so today I have connected the dynamo and will check tomorrow, The only thing not connected now is the horn.  We will see...........   Barry

Barry Wilson

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Nov 12, 2018, 12:56:45 PM11/12/18
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Hi Richard, Thats a great offer, however I live on the edge of the world in Lincolshire in Sutton on Sea.  Too far to expect you to do it, so I will soldier on but If I do come to a dead stop I will come down to you with vernier/paper/paper etc.

I really appreaciate the offer.

Barry

Barry Wilson

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Nov 12, 2018, 1:00:35 PM11/12/18
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No Slight Intended Andrew,  I still race  ( P6 parades ) more modern bikes. so love speed so it will do me good on the road to slow down a bit.  The electric route sounds complicacted and I have enough problems in the direction.

Barry

Andrew Nahum

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Nov 12, 2018, 3:32:36 PM11/12/18
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None taken I assure you!  The telescoping drive and a period speedo is a much more elegant solution. Do you feel like making two!?

Andrew 

Dirk Van Ussel

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Nov 12, 2018, 5:09:55 PM11/12/18
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Tried to take it apart but that didn't go/ Looks like it has been pressed together?On the bottom there is a metal part with a nylon insert. Behind the top is a brass(?) plunjer where the sliding is happening. For a 1 mm wall thickness tube it is quite heavy.µ

 
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Barry Wilson

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Nov 13, 2018, 6:44:48 AM11/13/18
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Hi Dirk.  Thanks mate, I didn't expect you to strip it, the internal drive must be two parts to allow the telescopic movement, I suspect the nylon bit you can see is probably a bearing with a nylon seal.  As there doesn't appear to be a drive slot of any kind in the inner tube along its length it must be in the upper drive shaft.  I wish I had x-ray eyes !!  The extra pics will help a lot.

Cheers Dirk

Barry Wilson

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Nov 13, 2018, 6:47:10 AM11/13/18
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Hi Andrew, I usually make a prototype first and then a final version, I usually make two of those in case I cock one up so assuming I don't screw things up I will let you know.  Thanks for your help.  Barry

Rick Yamane

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Nov 13, 2018, 10:57:42 AM11/13/18
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I would expect to find either a sliding hex or square drive coupling in there. Sourcing small hex or square bar stock is easy enough but do you have a way to broach the female side?

 

Rick

 

From: guzzi-...@googlegroups.com [mailto:guzzi-...@googlegroups.com] On Behalf Of Barry Wilson
Sent: Tuesday, November 13, 2018 3:45 AM
To: Guzzi Singles
Subject: [guzzi-singles] Re: Airone Speedometer drive

 

Hi Dirk.  Thanks mate, I didn't expect you to strip it, the internal drive must be two parts to allow the telescopic movement, I suspect the nylon bit you can see is probably a bearing with a nylon seal.  As there doesn't appear to be a drive slot of any kind in the inner tube along its length it must be in the upper drive shaft.  I wish I had x-ray eyes !!  The extra pics will help a lot.

--

Barry Wilson

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Nov 13, 2018, 1:23:49 PM11/13/18
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hexagon is possible, I can make a broach good enough for a few peices or at worst a good old hand file and a lot of patience. You are right hex/sq bar in stainless is easy to get. Thanks Rick.

Rick Yamane

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Nov 13, 2018, 2:08:21 PM11/13/18
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Well don’t forget, the broaching is going to have to be 3-4” deep. I don’t know what the fork travel is but it will have to be at least that much.

Paul Compton

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Nov 13, 2018, 2:27:57 PM11/13/18
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On Tue, 13 Nov 2018 at 19:08, Rick Yamane <ri...@motionpro.com> wrote:

> Well don’t forget, the broaching is going to have to be 3-4” deep. I don’t know what the fork travel is but it will have to be at least that much

The broached section only needs to be long enough to provide
sufficient drive/wear area. The rest can be clearance, although if its
bore is equal to the circumscribed polygon, it will provide additional
support.
--
Paul Compton
www.morini-mania.co.uk
www.paulcompton.co.uk (YouTube channel)

Rick Yamane

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Nov 13, 2018, 6:47:28 PM11/13/18
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Ah, I didn't think of that. I guess the female counterpart can be bored from the top as long as you allow sufficient drive area as you say. A cable drive can be brazed or welded to the top after the boring procedure.

-----Original Message-----
From: guzzi-...@googlegroups.com [mailto:guzzi-...@googlegroups.com] On Behalf Of Paul Compton
Sent: Tuesday, November 13, 2018 11:28 AM
To: guzzi-...@googlegroups.com
Subject: Re: [guzzi-singles] Re: Airone Speedometer drive

Barry Wilson

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Nov 14, 2018, 3:13:49 PM11/14/18
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I dont know what I am doing here, I just need to shut up and wait for you guys to desigh it for me, !!  Quite right Rick back boring is the answer. I am almost at the drawing board stage, just a few more wrinkles to wrap my head around.

Just a note regards the battery draining problem on the Airone, I have put it all together and all appeared well until I ran the engine and worked the horn  (Magneti Marelli 6v proper one ) the horn didn't work and it lit up the ignition light ??  I have disconnected the horn wires and everything seems great, no more juice loss.  I can now investigate the horn wiring. Back to the drawing board.  Thanks one and all for your help, no doubt this is the best forum on the net, well done.

I will let you know how I get on.  Barry

Barry Wilson

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Nov 14, 2018, 3:24:44 PM11/14/18
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Well spotted Paul, We used to have a circumcised parrot and ours flew off as well, bloody parrots !!  sorry I couldn't resist it :-)   Seriously I am grateful for any input, so thanks mate. I reckon 12mm length of drive is more than enough. I might even look at plastic/nylon materials for the inner sleeve. Talk later, Barry

Barry Wilson

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Nov 14, 2018, 4:37:27 PM11/14/18
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Hi Dirk, Can you tell me if the 140mm is overall length of the 7mm shaft as fully extended when on the bike or on the bench ?  I assume the knurled collar screws onto the top drive of the gearbox to hold the shaft in place. The top end of the output shaft looks odd ?  does it accept a sleeve with a locking side screw over it on the short bowden cable to the speedo, and if so what diameter is it.  Sorry to bother you but you seem to be the only guy with bits to measure.  Thanks in advance for any help Dirk.  Barry

Barry Wilson

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Nov 15, 2018, 7:28:50 AM11/15/18
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Hi Dirk, I have ordered the short speedo cable to suit so I can sort out the top connection from that so I no longer need the top end details. Sorry to mess you about.  Thanks  Barry

Barry Wilson

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Nov 15, 2018, 11:31:32 AM11/15/18
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Hi Andrew, Are you serious about wanting one ? if all goes to plan it will be a lot cheaper than the ones from Italy. There is no commitment but it will help me decide if I make three or two,  I have ordered tubing so I am definitely going ahead. I will only make the telescopic part and supply the top cable to the speedo, I will probably use a Smiths type speedo and get a Guzzi face but you would need your own clock.  At this point I am still drawing up the clamps but they look problematic as I need press tooling to form them properly, I seems they are not available online so I may have no choice but to go back to my old trade as a toolmaker. Take care   Barry

On Monday, November 12, 2018 at 8:32:36 PM UTC, andrew...@googlemail.com wrote:

Dirk Van Ussel

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Nov 15, 2018, 11:39:09 AM11/15/18
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Naked tube is 170 mm long,the top part 23 mm with 10mm thread. The bottom part is 10 mm. The 7 mm tube is 14 cm extended.
The inner tube is 12 mm diameter  with 6 mm wide slots.
I was able to pull it apart with the grease nipple removed .In the slot sits a sort of round brass part where I suppose the 7 mm tube is screwed in(bad foto)
On the top the exit part is round but pressed to form a 3 mm  square hole for the cable
Dirk
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Barry Wilson

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Nov 15, 2018, 6:24:05 PM11/15/18
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Dirk my friend you are a star, I couldn't work out how to create the square drive hole that way looks simple,  Dare I ask for one more favour ?  It would help to know the width and thickness of the clamp steel, I suspect 20mm wide and 3mm thick.  My design may be slightly different as i have found some bearings  which are perfect and are sealed against dirt but will still use the grease nipple. I am looking forward to the tubing etc arriving to get started.  Thanks a million.  Barry

Dirk Van Ussel

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Nov 16, 2018, 10:38:26 AM11/16/18
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19 mm wide and 2mm thick. 10 cm from point to point for the clamps.

Op zondag 4 november 2018 12:40:19 UTC+1 schreef Barry Wilson:
Does anyone have details of the telescopic drive unit so that I can make one ? e.g.  close up pictures/dimensions/etc would be brilliant. I have the hub gearbox fitted so only need the tubular section details.

Any help would be appreciated.

I don't know if any owners of Airone's would be interested in sets of the original material cork rear damper discs, ( not composite copies) they are just under 3mm thick. I have made the tooling to produce them and tested on my Airone and they work very well. About £19 a set plus postage, which should be very little due to the weight/size.  A set is 12 pieces, eight large ones and four small ones for the ends.

My Airone had mainly hardboard ones which were in poor condition hence the tooling. Will take some pictures if there is any interest.

I am not a dealer/shop/sellar etc. I just thought it might help other restorers, if not, no worries.

Dont forget the speedo drive info please.

Regards

Barry

Barry Wilson

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Nov 18, 2018, 7:33:04 AM11/18/18
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thanks for that Dirk, my bearings arrived yesterday and the tubing should be here this week, I will report progress as things go along.  Bye for now.  Barry

Barry Wilson

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Nov 20, 2018, 6:31:56 AM11/20/18
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All that makes sense Dirk, I am designing mine differently, I intend using ball races, not bushes, The 7mm drive shaft will be virtually the same as yours, could I ask if you could measure the overall length of the shaft and the length of the slot in the inner sleeve.   I am busy making the crimping tool today to form the square drive hole for the cable to the speedo. None of this would be possible without your help, thanks again.  Where do you live ?  Regards  Barry  p.s.  If you have already rebuilt it please do not strip it again, I will sort it by a bit of guess work ,,

Barry Wilson

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Nov 20, 2018, 6:40:17 AM11/20/18
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Hi Andrew, Did you pick up my answer regards a second unit ?  I don't mind if you don't want one, it will save me work, but I am more than happy to make you one.

The clamps will be the hardest parts due to having to make press tooling.  I wish I could find the supplier as the tooling must exist somewhere.  I will try to find him.

Regards  Barry 

On Monday, November 12, 2018 at 8:32:36 PM UTC, andrew...@googlemail.com wrote:

SED Sci

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Nov 20, 2018, 11:12:01 PM11/20/18
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Barry,
Would you post pictures of your manufacturing process?  (for example, what does the tool look like that makes the square drive?)  This reads absolutely fascinating but it's hard to visualize.  
Thanks,
Shawn

Paul Compton

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Nov 21, 2018, 3:20:12 AM11/21/18
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> Would you post pictures of your manufacturing process? (for example, what does the tool look like that makes the square drive?)

Some examples of cutting polygon holes from two of my favorite YouTube
machinists...

Making your own square push broach
https://www.youtube.com/watch?v=MYI1slVGziU

Testing a 'wobble' broach
https://www.youtube.com/watch?v=Vg7SCXOh-KY

Barry Wilson

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Nov 23, 2018, 6:56:14 AM11/23/18
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Hi Shawn,  I have now had chance to see the internals by Dirk sending a load of pictures, After buying the steel tubing I can now see that Guzzi made the drive a milled slot all the way through both sides of the inner tube which in my case will be 10mm o.d. and a 7mm bore. I will follow the Guzzi idea of putting a pin through the 7mm stainless drive shaft from the gearbox which will allow the 7mm sahft to slide up inside the 10mm x 7mm inner tube.  ( I will take pictures as I start machining , hopefully next week )  With regard to the 3mm square hole at the top for the cable inner,I am going to make a crimping tool to use in my bearing press and squeeze the 10mm x 7mm tube into a 3mm square centre section by inserting a 3mm square solid bar down the centrre to keep the size accurate.

I have spent £58 on a set of original clamps from Italy, I hope to make a press forming tool to make more but to the precise design and sizes. It is costing more than I hoped but am in too far now to chicken out and should I decide to do another single Guzzi I can produce more economically.    I understand some people will get bored and rightly tell me I am tight !  I am on a state pension and my wife insists on eating so needs must, as they say..  Bye for now  Shawn.

Barry Wilson

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Nov 23, 2018, 7:10:21 AM11/23/18
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Hi Paul,   Thats really interesting, I love his versatile lathe, I have never seen one in the U.K.   Fortunately it is easier for me to make a forming tool in the Bridgeport by milling two V cuts across two bits of 10mm thick steel and squeezing the tube into a square internal shape, However I had never thought of making a broach myself, I am not sure how easy it is here to get a carbon tool steel suitable for hardening in small pieces. Thanks for your input, it all helps.  Barry

Paul Compton

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Nov 23, 2018, 8:35:26 AM11/23/18
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On Fri, 23 Nov 2018 at 12:10, Barry Wilson <mrsh...@gmail.com> wrote:

>Thats really interesting, I love his versatile lathe, I have never seen one in the U.K.

The Sherline was reasonably common in the UK and I've seen a couple of
examples. It's still in production.

> However I had never thought of making a broach myself, I am not sure how easy it is
> here to get a carbon tool steel suitable for hardening in small pieces.

Gauge plate is readily available. It is available in squares, but much
easier to find as flat stock from which you could saw a square
section.
Metal Supermarkets apparently have square section O1 available.

Failing that, one of Chris's more recent videos, part of his
Antikythera series, shows the process of carburising mild steel to
make files.
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