Ray's Variant of Peter Head (Fully Laser Cut)

[Ray Kholodovsky]

Hi Folks,

With Peter's help I've made this entirely laser-cuttable variant of his head design, right down to the "custom" gear which is press fit onto the motor shaft.  I like it when machines handle the manufacturing and so was off put when I saw that his design required drilling and tapping holes in the side of the material - I didn't have any way to do that accurately and I wanted to use a thinner material (6mm instead of 9mm) which might crack when attempting this.  I suggested what I've seen every other laser cut assembly do, this sort of "T" shaped captive nut trap which the laser cuts along with everything else.  And so, here we have the head with the first set cut on my laser from 6mm MDF, and temporarily doing a test fit with MGN7 rails I had on hand.  The design calls for MGN9 though and I am waiting for those to arrive, as well as the optical endstop, before I can do much else.  

Here it is mounted to my new PnP frame in the works, with an adapter plate to go from the openbuilds micro v plate design I cnc'ed from garlite X to the MGN12 trolley mounting hole pattern. (The main head is designed for the Anthony Webb rail type machine, so the MGN12 trolley will mount directly to it for the X axis).

Here are some shots of my 40w laser (driven by custom made control board running smoothie firmware) at work and some of the assembly shots. 

Oh, and the gear and rack all cut perfectly and mate/ interact well.  I handle my laser cutting much like CNC meaning that I offset for kerf by doing everything as an inside or outside profile with a .0004" (~0.1mm) tool diameter, in Vectric Aspire with a PostProcessor I wrote for the laser (which takes gCode due to the smoothie upgrade). 

Let me know what you all think and a big thanks to Peter Betz for his initial design work on this as well as the ongoing collaboration. 

Cheers,

Ray

[Anthony Webb]

This is pretty sweet. If anyone posts to ponoko and has a cart saved for others to purchase let me know. I'd definitely be interested in trying one. If it works it is definitely a huge cost saving over the $300 robot digg head. Such a great community effort pushing this thing forward. 

Sent from my iPhone

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[rayk...@gmail.com]

Anthony I'd be happy to cut you a set from cast acrylic. I could do it now if you want to be a really early tester or you can wait until I get the remaining parts in and actually test this thing. 

My laser is tuned to 2 thou dimensional accuracy! 

Ray

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[Anthony Webb]

I don't mind being an early tester. Ping me with the details. 

Sent from my iPhone

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[Anthony Webb]

Are you mounting the camera on this head?

Sent from my iPhone

On Jul 31, 2016, at 2:07 PM, rayk...@gmail.com wrote:

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[Ray Kholodovsky]

Oh, yes, good call.  I need to "port" the mounting plate to this nut trap design and then I will show what it looks like. It will be a flat plate with 4 tapped holes to receive M3 screws holding the camera.  I expect to include nylon spacers as well, to keep the camera at a fixed length from and square to the plate.

[Andrew Frazer]

If you are using cast acylic, just be very cautious about the thickness of the material and how consistent it is.   The casting process often produces material is that is dimensionsally variable.     It often can be as much as +/-0.5mm    This may not be an issue, but keep it in mind.

[rayk...@gmail.com]

Yep, that's consistent with what I measured on my sheet of cast acrylic. 

Think Delrin is a better choice? 

Ray

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[Andrew Frazer]

You can get extruded acrylic sheet and it will be dimensionally consistent. It also costs  more.  

This stuff might be ok for low duty cycle stuff...

[DAniel Dumitru]

I don't know if Delrin can be lasercutted.

I see that you have modified a bit Ray's design. Could you please share
those changes ?

For anyone in Europe I will cut those for free including classic postage.

BR
Daniel

On 01/08/2016 1:22 AM, rayk...@gmail.com wrote:
> hat I measured on my sheet of cast acrylic.
>
> Think Delrin is a better choice?

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[Andrew Frazer]

Delrin cuts ok, but again its full of stress' when its extruded.. so be careful, you might just have the thing crack one day.

[matt]

Is there a reason why people are shying away from having this reproduced
in aluminium? I can't imagine weights a particular issue - the Juki 460
head was aluminium with centering jaws, multiple air solenoids, and that
machine was rated for 2800 cph.

Since I've done Peters design as a 3d print for proving the prototype,
i've now moved to getting it reproduced in aluminium.

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[Andrew Frazer]

Peronsally i woud'tn contemplate doing this in acrylic or MDF.   For the small increase in cost for doing it in Alumium ( I'll use 7075) I dont' get it, given all the risks that acrylic poses..  I might be wrong, but its a question of "when" rather than if it will wear out or break... 

But if you are trying to do a $400 machine, then this is one way of saving the $10's you need to do.

[Peter Betz]

Looks good Ray, those nut traps are a great improvement.

Regarding the aluminum, myself and Mark are currently working on producing my head design in aluminum on a 5 axis water jet. I will start a new thread once we have some more info to share. This will be a group buy situation. Looking forward to a full-metal variant ;)

Peter.

[cf]

I think stainless is more suitable for laser cutting compared to aluminum, but if there are group members that has access to water jet and that can provide a group buy of aluminum parts then that would be my preferred option.

[Paul Jones]

My reason is I can't be bothered as I think it's overkill. Each head only weighs 10's of grams, the whole assembly is about 400g including the 3 stepper motors, and there are no significant dynamic forces. Thousands of people have 3d printers made from acrylic and there is no known structural problem with them (that I know of). Getting things laser cut is significantly easier than water jet cut.

I notice there are a lot of "engineer" types on this list who need to have the technically correct solution, I'm obviously not one of them :) (although I do have an engineering degree). My judgement is that acrylic is more than good enough to get the spec I want with the reliability I want.
But aluminium would look great!

Paul.

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[Mark Harris]

I have a pretty nice Omax waterjet at work, so Peter and I are looking at using that for Aluminium. Aluminium is cheap and suitable.. the waterjet will go through upto 3 or 4" of steel pretty happily though (that's the max head height), so we could really run it out of anything that is cost-appropriate. The software auto-compensates head angle to ensure the edges are perfectly perpendicular to the face.

Waterjet cut parts is no effort for me, it cuts 1/4" steel faster than I can cut 1/4" acrylic on a 120W laser :)

When Peter creates his thread we can discuss materials for waterjetting, so as not to take Ray's thread off topic.

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[Paul Kelly]

I’ve never really understood the obsession with aluminium for cnc machines of any type. Granted it’s stiffer than plastic, and more dimensionally stable than wood. But the thermal expansion is a killer. You might get away with it if your bearing elements are Al too, but they are usually steel.

 

To illustrate by example:

If you have a 500mm long bit of some Al extrusion, with a steel linear bearing bolted to it and the temperature changes by 20 deg C the linear bearing will be 100um shorter than the aluminium rail. This will cause it to bend or work loose. In a poor design these mis matches can add up.

 

The other issue is the dynamic effects and structure resonance.  “Everything flexes and no-one believes it” is a bit of a mantra in mechanical design. Light, stiff structures have high resonant frequencies and are hard to damp. Heavier stiff structures have lower resonant frequencies and deflect less. (this is more of an issue for cutting machines, but we see it in our laser cutter)

 

Oh, and steel is HEAPS cheaper than Al, much easier and cheaper to weld (where you can tolerate or machine out the warping), and easier to bend and form...  

 

Besides all that, Steel has nothing really going for it J

 

 

Paul Kelly | Design Engineer
CASWA Pty Ltd
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From: ope...@googlegroups.com [mailto:ope...@googlegroups.com] On Behalf Of Mark Harris
Sent: Monday, 1 August 2016 5:05 PM
To: ope...@googlegroups.com
Subject: Re: [OpenPnP] Ray's Variant of Peter Head (Fully Laser Cut)

 

I have a pretty nice Omax waterjet at work, so Peter and I are looking at using that for Aluminium. Aluminium is cheap and suitable.. the waterjet will go through upto 3 or 4" of steel pretty happily though (that's the max head height), so we could really run it out of anything that is cost-appropriate. The software auto-compensates head angle to ensure the edges are perfectly perpendicular to the face.

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[Ray Kholodovsky]

That's the general idea here: Peter and Mark will handle the aluminum variant of this, and I'm more than happy to cut a set from acrylic for anyone who may want one. The way I see it there will be some people that want the metal version, some people that are cool with acrylic, and some people that will say neither is suitable for their desires/ material science beliefs.  That's totally fine.  

That said, I want Peter and Mark to succeed on their first try, and me offering to cut a few sets out of acrylic to willing testers who can provide early feedback is a cost effective way to do that.  

Daniel, I think you meant to say that I, Ray, have modified the original design from Peter.  When it's tested at least once I would feel comfortable releasing the files.  It's not even done yet - there are still changes I intend to make. 

[Mark Harris]

PK,

My main concern with steel is corrosion, sure it's easy enough to keep coated in oil but if you miss a bit, then you get rust ;) These parts are small enough that there will not be any noticeable thermal expansion during operation.

Stainless steel was specifically asked for, and thats not something that is readily stocked at the place that will sell me small pieces of a plate, so we'd need to buy a full sheet and thats really expensive. I know we have 1/4" 6061T5 and 7075 around the workshop I can use, but I'm not sure we typically have steel that thick (sheet yes, plate no)... but I havent really looked through the plate storage to see whats around, I just know we have some 60thou stainless because I used it on Friday. Damn these Imperial measurements drive me nuts.

As a comparison for steel vs aluminium, randomly picking a plate size here...

STEEL-HOT ROLLED PLATE A36, 10"x30" is 65.22

ALUMINUM PLATE 6061T6, 10"x30" is 103.80

Prices in store are always different to the online price. The larger the piece the bigger the gap (at 10x10" the difference is only 5%).

Those are the only materials that I can quote in 1/4" plate online.

Like I say, when Peter is ready to post his thread we'll discuss materials there, we may not be getting enough material to make a cost difference for steel, and if our run is small, then it may be worth just using some offcuts from a larger plate if they are available, and paying work for them :)

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[alexander...@gmail.com]

A suggestion / request for anyone planning to offer a kit of parts or group buy opportunity in the future....

I (and I'm sure others) will be grateful if you would consider including all custom parts required for an Anthony Webb rail type machine in addition to the parts required for the new head design.

Thanks.

Alex

[rayk...@gmail.com]

Hi Alex, 

In looking at Anthony's BOM it seems the "custom" parts are set of CNC milled brackets. I suppose if Mark is going to be firing up the waterjet he could get some of those plates cut from alum if there was demand. 

As for me, I have a K40 laser and a ballscrew driven 3040 CNC along with my printers so I could make these parts if anyone wanted.

I understand the correlation but they'd still be separate products/ sets, but could possibly be purchased together. 

So, let me know if you need anything made. 

Ray

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[Peter Betz]

Yes we are also looking at waterjet parts for Anthony's design, with CNC'd features as required. I haven't checked in with Anthony yet though, so not sure if that is going to happen.

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[Anthony Webb]

The more the design is used and improved upon the better!  I created it with this in mind.  I'm excited to see the advancements in head design and recent feeder designs as well.  I feel like once feeders are solved we'll all have a nice starter platform for anyone who wants to do this stuff to have good success.  Nearly there!

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[John Reichard]

Is there a download for this?