Fastback seatpost binder retrofit ideas needed

[Tom T]

I have this vintage Peugeot 84 PSN 10 that I like the ride, except that it has an ATAX quill

seatpost that weighs about 3/4 lb., I'm thinking I can use a normal post by adding a

through -the- stays binder, and slot the seat tube between the stays.

The stays are 12mm dia. the binders I can see that works are more like the rack bosses or the water bottle bosses, one on each side and a long bolt, ( about 25mm) their shaft dia. is small enuf, but they use M5 bolts instead of the normal M6 for seatpost binder.

This is the most unobtrusive way I can see of all the different options I've seen and considered.

Questions:  

-  Is M5 bolt strong enuf, or do I need make 2 binders ?

-  What other binder can I use with these skinny stays to make this work?

-  What do I need to watch for when doing this?

TIA for your help.

Tom T

SF Bay Area

[M-gineering]

Leaving questions of originality aside, m5 as a binder bolt is probably
fine if you can assure is only tensioned in a straight line and not
subjected to bending. Given the nature of a seatclamp that is unlikely ;)


It doesn't sound like you have access to a lathe (you should!) so then
your best course of action is probably to drill a 8mm hole through the
stays, braze in a 8x1mm tube, square up the ends, slot the seattube and
run an M6 bolt & nut through it.

On 12/7/2023 10:28 PM, Tom T wrote:
> I have this vintage Peugeot 84 PSN 10 that I like the ride, except that
> it has an ATAX quill
> seatpost that weighs about 3/4 lb., I'm thinking I can use a normal post
> by adding a
> through -the- stays binder, and slot the seat tube between the stays.
>
> The stays are 12mm dia. the binders I can see that works are more like
> the rack bosses or the water bottle bosses, one on each side and a long
> bolt, ( about 25mm) their shaft dia. is small enuf, but they use M5
> bolts instead of the normal M6 for seatpost binder.
> This is the most unobtrusive way I can see of all the different options
> I've seen and considered.
> Questions:
> -  Is M5 bolt strong enuf, or do I need make 2 binders ?
> -  What other binder can I use with these skinny stays to make this work?
> -  What do I need to watch for when doing this?
> TIA for your help.

> 52285527937_885a1465e5_c.jpg52285527927_cb7b2fba31_c.jpg

> Tom T
> SF Bay Area
>

--
mvg

Marten Gerritsen

Kiel Windeweer
Netherlands


***********************************************************************
Tubes & Coffee
Zondag 17 December weer de traditionele open dag in de werkplaats

***********************************************************************

[Andy Newlands]

Hi Tom,

Marten is absolutely correct.  5mm binder bolts can be insufficient.  Not exactly comparable but my prototype top stay 8mm binder bolt on a Strawberry I rode on a Super Tour back in the day could not handle the load.  I switched over to a 10mm button head cap screw to solve the problem.

http://www.strawberrybicycle.com/gallery/view_photo.php?set_albumName=Mechanique&id=csc01

Cheers,

Andy

Terra Nova Cycles LLC

1535 SW 17th. Ave.

Goose Hollow

Portland, OR 97201

503-224-1215

an...@strawberrybicycle.com

www.strawberrybicycle.com

www.torchandfile.com

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[Tom T]

Thank you Marten, that sounds like a good plan.  My friend has a lath in his garage and that's where we will do this. I just need to get the 8 x1 tube.

Thanks Andy, I'm not carrying any loads on this bike, besides, I'm a small guy, never had any problem with M6 binder bolt, but I'll keep your note for future reference.

Tom

[Tom T]

FWIW,  my travel bike has a Ritchey Breakaway seat lugs and they use 5mm bolts. 2 of them,

[Michael F.]

Even as a Pooch-o fan, it seems like a really difficult and tricky modification to actually make work. 

First - is there enough room to cut a "decent" 4mm slot between the seatstays where they join the 

seatlug ? 

As an alternative i'd suggest perhaps investigating other internal seatposts that weigh less. American Classic had one a while ago, and there were also ones that were used in the 90's on Gianni Bugno's lugless Moser frames. Maybe those were by Selcof ? You might have to modify a 27.2 to a different smaller diameter, but on the positive side you'll save the original paint !

Good Luck !

michael in SF

Sent from my iPhone

On Dec 7, 2023, at 3:23 PM, Andy Newlands <strawber...@gmail.com> wrote:

Hi Tom,

To view this discussion on the web visit https://groups.google.com/d/msgid/framebuilders/9FB72A2A-526B-400B-8AA2-B50FB8034FAE%40gmail.com.

[M-gineering]

On 12/8/2023 3:05 AM, Michael F. wrote:
>
> First - is there enough room to cut a "decent" 4mm slot between the
> seatstays where they join the
> seatlug ?

> 4mm is excessive in my book. If everything fits 2mm is fine

[Jim Adney]

On 7 Dec 2023 at 15:23, Andy Newlands wrote:

> Marten is absolutely correct. 5mm binder bolts can be insufficient. Not
> exactly comparable but my prototype top stay 8mm binder bolt on a
> Strawberry I rode on a Super Tour back in the day could not handle the
> load. I switched over to a 10mm button head cap screw to solve the
> problem.

Long ago, I found that the clamping force required depends almost
completely on how round the tube opening is. Production frames tend not to
be reamed after brazing, so the opening is warped and large clamping
forces are needed. If the tube is carefully reamed, light force will do. The
difference will probably be 0.010" or less, but the effect can be huge.

--
*******************************
Jim Adney, jad...@vwtype3.org
Madison, Wisconsin, USA
*******************************

[Jim Adney]

On 8 Dec 2023 at 7:48, M-gineering wrote:

> 4mm is excessive in my book. If everything fits 2mm is fine

2 mm is plenty if the hole is round and the seatpost is a good fit. Production
frames seldom get reamed and they get a slightly undersided seat post to
compensate. The result is the need for a wide slot in the seat lug and lots of
clamping force.

[Tom T]

I agreed, last time I did this I just doubled up on the hacksaw blades and it worked just fine.

Tom T

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[riendeau...@gmail.com]

Do the math on the comparative seat post weight.   You may be doing a lot of work for very little or no reduction.

[riendeau...@gmail.com]

I think the way to get a "normal" seatpost on that frame is to sleeve the top with maybe 2 to 3 inches inside the tube and put something like this on the tube you sleeve in.

 https://framebuildersupply.com/collections/seat-collars/products/28-6-27-2_seatclamp 

Thomson makes a high end seat post in 25mm diameter.  

[Tom T]

Riendeau,  Thanks for the idea.  

I actually have that binder in my stash, left over from the first frame years ago.  I'm thinking the gap between it and the sleeve would be too much, it's metric size tubing so the seat tube is 28.0.

MBK in the 80s used to braze the binder under the fastback stays, ugly but works and probably easier to do since there's no hole thru the stays to drill.

To your previous comment, the weight saving is significant since I only need a handful of seatpost showing on this bike, the rest is burried ( about 8").  3 inches insertion is more than enough for me, the rest can be chopped.  I'm thinking of using the same post without the quill bolt, the cone wedge and split sleeve.

Tom T

Alameda Ca

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[Dan Chambers]

" MBK in the 80s used to braze the binder under the fastback stays, ugly but works and probably easier to do since there's no hole thru the stays to drill. "

Like this?

All the best,

Dan Chambers

[Tom T]

That’s the one.

Sent from my iPhone

On Feb 12, 2024, at 09:16, Dan Chambers <dancha...@gmail.com> wrote:



" MBK in the 80s used to braze the binder under the fastback stays, ugly but works and probably easier to do since there's no hole thru the stays to drill. "

Like this?

To view this discussion on the web visit https://groups.google.com/d/msgid/framebuilders/80f8a7e0-d7ba-43b0-9ebd-29184bf7a3c9n%40googlegroups.com.

<424866437_10226052950444406_6920407706110678474_n.jpg>

[Tom T]

And then there’s this one-

Sent from my iPhone

On Feb 12, 2024, at 21:08, Tom T <vel...@gmail.com> wrote:

That’s the one.