Alternatives to aluminum angle and channel in McWire?

[Aggh! I lost another really long post to the caffeine monsters (tab closing, anyone?), so this one is going to be short, quick, and choppy. Sorry.]
[All part numbers are McMaster's [www.mcmaster.com].]

Does anyone know what I can use as a suitable replacement of the 1/8" thick aluminum angle and channels in the McWire [www.reprap.org]? The angle (#88805K57) is $25.95 and 96" long (I only need 43"), and the channel (#9001K34) is $22.63. The total is $48.58, which is significant compared to the total price of the project.

Anyone have any ideas for alternatives?

The angle seems to just be a structural support for the channels and the motors. Perhaps I could use wood (like plain 2x4)?
Or perhaps I could use rounded angle (#8982K134)? It's available in 48" lengths (as opposed to square which is only available in 96" lengths) and is about the same price per length, and thus is about half the price ($14.54) of the square (as I only need 43" anyway).
Or perhaps square perforated steel angle (#8968K26)? It's only $8.66 for 72". The steel is a bit thinner, but since it's steel, could it be strong enough anyway? Or does the "perforated" part cancel this out?
The docs specifically suggest against using thinner (1/16" thick) aluminum angle, so I wasn't planning on using that (unless it's the best option; if it is, please say so).

As for the channels, they seem to be a sort of linear guide and bearing combination. Really radical idea - could I use wood and spray on paint or something to make it work alright? Or some cheap lubricant?


Other than stuff like that, I'm kinda out of ideas that *might* work.

Any suggestions? Or should I just bite the [umpteenth] bullet?

[Also note that as to the motor mounting, I'll be using (modified and encoded) GM3's.]

Oh, don't bite the bullet on this one. I have the afore mentioned expensive channel and angle set up on my repstrap. Works okay but there is still a bit of friction there that I don't like and that we could reduce and save ourselves some angle doing it.

Use wood and a few slivers of PTFE that you should have already bought for other places. Bolt on the wood and apply a few little vertical strips of PTFE as a spacer between the wood and the channel. All you really need is a flat surface for the PTFE to rub against and the channel--or even the angle--will work fine for this.

Also, don't bother bolting the PTFE strips to the bed as in the official McWire. Seems like a waste of hardware IMHO. I super glued mine to the bed. Worked fine--superglue sticks to teflone well--and doesn't seem to be wearing at all after maybe 50 hours of running back and forth. And even if it does wear, you can replace it. I have a nice huge sheet of PTFE that I can keep drawing from for a LONG time.

My two bits.

Demented

Check your yellow pages for a local metal shop that will sell you scrap on the cheap - most big cities in the US will have these kinds of stores. I usually hit up a place called "Metal Shorts" whenever I need stock metal for small projects, as they're about 40 minutes from my house and can usually give me a pretty good deal on scrap. Just from looking at the design, I could probably get all the metal you need for the McWire for around $20, in shorts of various lengths.

I wouldn't recommend using wood or rounded angle - this needs to be the highest-tolerance part in your entire assembly, and I get the sense rounded angle is usually made to looser tolerances. Could just be me though, or the particular pieces I've seen.

You could try onlinemetals.com as another supplier - that's what I do when I need a specialist item that the local shop doesn't have. They have a huge variety and decent prices, so it's worth a shot. Shipping is going to be expensive though, same as McMaster.

Demented Chihuahua Wrote:
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> Oh, don't bite the bullet on this one. I have the
> afore mentioned expensive channel and angle set up
> on my repstrap. Works okay but there is still a
> bit of friction there that I don't like and that
> we could reduce and save ourselves some angle
> doing it.
Alright. Thanks for the info in your post, but some things are still not so clear to me.

> Use wood and a few slivers of PTFE that you should
> have already bought for other places.
Do you mean the 1/8" thick, 1/2" wide PTFE strips (#8735K11)? I wasn't going to have any left over, so do you mean I should order extra? Or are you referring to something else? (And of course, if you mean the strips, I assume you mean I should cut some into tiny "sliver" widths.)
> Bolt on the wood and apply a few little vertical strips of
> PTFE as a spacer between the wood and the channel.
Do you mean cut thin slices, say 1/8" to 1/4" wide (and of course 1/8" thick), and then place long lengths of these on the sides of a 3/4" thick piece of wood, forming a U with the PTFE on the sides and the wood on the bottom? The PTFE sides would then contact the PTFE bearings on the stages, and the skate bearings would roll along the sides of the wood. Perhaps I should also put similar PTFE strips along the sides of the wood, so that the skate bearings glide along PTFE instead of clunking across wood? Or would the wood alone be okay?
Or am I totally misinterpreting what you were saying?

> All you really need is a flat surface for the PTFE
> to rub against and the channel--or even the
> angle--will work fine for this.
Hm? The channel/angle thing is confusing me, I thought we were doing away with both?

> Also, don't bother bolting the PTFE strips to the
> bed as in the official McWire. Seems like a waste
> of hardware IMHO. I super glued mine to the bed.
> Worked fine--superglue sticks to teflone well--and
> doesn't seem to be wearing at all after maybe 50
> hours of running back and forth.
Hm, gluing is interesting, but it may be easier (for me at least) to just use bolts where I can (though I may have to use glue the above mentioned wood-teflon "channels").
> And even if it does wear, you can replace it. I
> have a nice huge sheet of PTFE that I can keep
> drawing from for a LONG time.
Lucky you.


Another thing - if I'm right in thinking that you're suggesting using a piece of wood with ptfe strips placed on top as a replacement for the aluminum channel, and you're right in thinking that it will work, then for the aluminum angle replacement (the thing for stabilizing the rails and mounting the stepper/opto endswitch), could I just bolt on a piece of plywood (which I'll have scraps of) vertically?


Oh and one last thing - with the PTFE on wood thing, unless I use fairly thin strips (like 1/8" thick by 1/16"-1/8" wide) the added cost of the PTFE will go up fairly quick (if I use 1/4" wide strips the price might approach or pass the price of the aluminum).
So am I missing something (that is, is my whole understanding of your suggestion flawed)? Or should I just cut some really thin strips ?

Okay, regardless of whether or not this is what Demented had in mind, this is what I plan to do:

Instead of the 96" of channels (4 13" lengths, 2 21" lengths [www.reprap.org]):
1/2" plywood (yes, some of the scrap from the 1/2" backplate) is cut into 3/4" wide strips.
1/8" thick 1/2" wide PTFE bar (#8735K11, the same as used for the bearings) is cut into 1/8" wide strips (4 1/8"-wide strips out of a 1/2"-wide bar, obviously). Alternately, you could get these strips (using supplies from McMaster) a few different ways, each of which has its advantages [the "# Strips" column describes how many 1/8" wide strips I would be able to take from that width]:

Thckness	Width	Basic Cost 	# Strips	Cost Per Strip	Notes
1/8"	1/8"	$5.13/ft		1	$5.13/ft		Expensive, but already cut to the size we need.
1/8"	1/2"	$3.46/ft		4	$0.865/ft		Cheap, and only two strips from the center.
1/8"	1"	$5.54/ft		8	$0.6925/ft	Cheapest but strips from center might be uneven.

1/4"	1/4"	$7.74/ft		2	$3.87/ft		Higher price;  thicker means a deeper channel.
1/4"	1/2"	$6.93/ft		4	$1.7325/ft	Cheaper but the center strips might be uneven.

If we had 1/8"x1/4" strips, we could place them on the plywood and give it the same height as the aluminum channel, but they don't sell that size, so we would have to cut it ourselves either out of the 1/4"x1/4" or 1/4"x1/2". These of course are more expensive than the 1/8" thick, and I don't think it's worth the extra cost to make it the same height if we have to cut it anyway.

Personally I think the best balance is the 1/8"x1/2", which doesn't require too many cuts out of the center of the bar and is still reasonably priced. Plus, you're already buying some of this (for the stage bearings).

In any case, I'll take the 1/2" wide bar, cut it in half, and then cut each half in half, yielding the 4 1/8" wide strips.

I'll need the following pieces:

Description		Qty
plywood 1/2" x 3/4" x 13"	4
plywood 1/2" x 3/4" x 21"	2
PTFE 1/8" x 1/8" x 13"	8
PTFE 1/8" x 1/8" x 21"	4

corresponding to the 4 13" lengths and 2 21" lengths of aluminum channel I'm replacing. The total length of 1/8" x 1/8" PTFE is 188", meaning I'll need 47" of the 1/8" x 1/2" PTFE bar (I'll buy 4 feet, giving me an extra inch to play with).


I'm still a little bit sketchy on the attachment of the PTFE strips to the plywood. I first thought I should use ANSI 0-80 screws (91792A071), which would fit nicely through the center of a 1/8" thick PTFE strip (the screws are 0.06" diameter, leaving 0.0325" on each side of the screw). I would use one washer (92141A002) between the screw head and the PTFE, and one washer between the nut (90480A001) and the plywood.
[Seeing that there are 6 rails that each have 2 strips, each of which needs 2 connections, I'd need 24 screws, 24 nuts, and 48 washers. They all come in packages of 50 or 100, so one pack of each should be fine.]

The problem with this is that the screw head (0.039" or 5/128" tall) would be sticking out of the top of the PTFE strip. It would interfere with the stage when the stage reaches the end of the channel (and the PTFE bearings on the stage slide into the screw heads). I think this would be a problem, as the stage could never reach the endstops (or would go *bump* every time it did, possibly causing problems with the other axes).

If I use flat-head screws (91781A071) instead of the pan screws, and I don't put a washer under the head, could I perhaps screw the screw tight enough that 0.035", 82

>
> Or I could just glue the PTFE down, but I'm afraid the glue between the plywood and the PTFE might make the top surface of the PTFE not be flat anymore (though I suppose the wood itself might contribute more to this than the glue).
>

I think you'll find that you can't glue PTFE.

Forrest Higgs Wrote:
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> I think you'll find that you can't glue PTFE.

Can't you get furniture coasters that are essentially PTFE skids attached to a rubber backing? I've used some before, and they seem to be suck together with some sort of adhesive. I'd imagine there's *something* you could find that would work with it, although I don't know what.

I'd bet the coasters are on HDPE pads rather than PTFE. HDPE is about as slick at PTFE costs a pittance by comparison.

Mind, it's hard to glue HDPE, too.

I talked to a plastic pro the other day, asking him if he could offer a 60x60 cm board of ptfe in about 2cm thick (blueeyed as i was) he told me the price and weight of that item (enormous!, both!) and so i asked if he had an 2mm sheet that i could glue onto mdf or something.
He told me, that he personally had tested with sorts of glues and 1 and 2comp epoxys to glue ptfe onto something because of various requests of the same sort
without success.
he suggested screwing!

to glue hdpe you'll have to prepare the hdpe with (don't know what it's called in english.. :H2SO4 / CrO3) chrome sulfuricacid ?! nevermind.. that kind of stuff,
Or you can prepare it with highpressured plasma or lasers.
After that you can glue or print on it


'sid

Interesting. Out of curiosity, does anyone know how they get it to stay on those non-stick pans?

afaik it's first primert(with whatever) then coated(with liquid ptfe) and then burnt at about 420

Edited 2 time(s). Last edit at 07/31/2008 09:05PM by sid.

Well, this is rather good news I think. It gives me a convenient excuse to not use glue (for some reason, I seem to hate glue) - the fact that it wouldn't work anyway .

The countersink and 0-80 flat head screws (#91781A071) should work fine though, provided I'm careful when countersinking.

... i have pieces of PTFE-coated glass-fabric with a glue-back, so it's simply used like normal self-adhesive - should be common in hardware-stores i think ...

For bulk-PTFE-blocks/stripes i use screws only ...

Viktor

@Forest

You can glue PTFE. I don't know why the common conception around here is that you can't. I realize it is the "non stick" shit and all but I've glued it before to my RepStrap. Printed things on it and everything.

@ Joshua

I assure you that Super glue works on PTFE. If I'm wrong--I'm not--I'll pay for your mess up. Guaranteed.

My camera is down but here is a picture with where the PTFE was placed on my reprap. Your configuration may be different but you will get the idea and can modify it to fit your situation.

reprapptfeplacement.bmp

Substitute as much wood for channel as you can. Things don't need to be great. Just good enough to get you a Darwin printed.

Demented

Demented,

Interesting. Do you have any pics of parts you've printed with this setup?

Kyle

Posted on the builder blog about my progress. Prints there or here:

[picasaweb.google.com]

The picasa link has all the pictures I have. Haven't been printing in a while cause life and school caught up with me. Hope to get back to it soon.

Demented

A bit of a cool idea I came up with while refining my extruder parts list:

Instead of bolting the PTFE strips onto the wood rails (with 0-80 flathead screws), perhaps I could use the "Super-Slick Tape Made with Teflon

Edited 1 time(s). Last edit at 08/03/2008 04:02AM by Joshua Merchant.

IMO the plywood would be flat/smooth enough if you sanded it before installing and didn't torque those bolts down too hard. Keep in mind, however, that I'm only speaking to building a machine good enough to print the parts for a Darwin. I've had exactly zero problems with my cartesian bot--shitty and haphazard as it is--and many problems with my extruder. The bot is good enough--over good enough--but the extruder could stand some work. But that's been everyone's experience I think.

As for the PTFE tape...are you thinking about putting down a long strip of this over the whole length of the wood? or just little strips like I did on mine. If it is the long strip, this should work fine. If it is little strips like I did on mine, that might not work but I'm not 100% sure.

Sounds like you are doing a massive amount of work. Keep it up!

Demented

Demented Chihuahua Wrote:
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> IMO the plywood would be flat/smooth enough if you
> sanded it before installing and didn't torque
> those bolts down too hard.
Excellent.
> Keep in mind, however,
> that I'm only speaking to building a machine good
> enough to print the parts for a Darwin. I've had
> exactly zero problems with my cartesian
> bot--shitty and haphazard as it is--and many
> problems with my extruder. The bot is good
> enough--over good enough--but the extruder could
> stand some work. But that's been everyone's
> experience I think.
That's certainly interesting... I'll mull over it for a while.

> As for the PTFE tape...are you thinking about
> putting down a long strip of this over the whole
> length of the wood? or just little strips like I
> did on mine. If it is the long strip, this should
> work fine. If it is little strips like I did on
> mine, that might not work but I'm not 100% sure.
Yeah, a single strip placed over the entire length of each rail. If I only partially covered the rails with the tape, the PTFE bearings on the stages would be sliding across plywood part of the time.

> Sounds like you are doing a massive amount of
> work. Keep it up!
Heh, thanks.


I'm still curious as to whether anyone has an objection to replacing the 1/8" thick PTFE bar used as bearings on the stages with the 0.003" thick PTFE tape. Is there any reason it would be a problem?

Joshua Merchant Wrote:
-------------------------------------------------------

> I'm still curious as to whether anyone has an
> objection to replacing the 1/8" thick PTFE bar
> used as bearings on the stages with the 0.003"
> thick PTFE tape. Is there any reason it would be a
> problem?

By all means, try it and report back whether it works. It has been a long time since I have used PTFE tape - does it feel physically slippery? If so, I think you've got a reasonable chance of success.

Kyle Corbitt Wrote:
-------------------------------------------------------
> By all means, try it and report back whether it
> works. It has been a long time since I have used
> PTFE tape - does it feel physically slippery? If
> so, I think you've got a reasonable chance of
> success.

No idea. Up until today, my entire involvement with the RepRap project has been limited to the interior of my brain . I am ordering the tape today from McMaster (with the rest of the stuff), and I'll report back my findings.

It should work though, because the first two words in the item name are "Super-Slick" (#6305A12).

You're ordering PTFE tape from McMaster?

It ought to be available for cheap in most hardware or plumbing stores, assuming you're in the U.S. or some other western country.

Kyle Corbitt Wrote:
-------------------------------------------------------
> You're ordering PTFE tape from McMaster?
>
> It ought to be available for cheap in most
> hardware or plumbing stores, assuming you're in
> the U.S. or some other western country.


Sure, but is it "Super Slick"? The stuff from McMaster is $8.40 per 5yd roll because it's a 1" wide specialty tape. They do sell the normal plumber's PTFE tape for sealing pipe threads, too, which is probably what hardware stores have, but this is not the same thing. (I'm actually buying this from them as well and not Lowes because they are probably cheaper at $1.13 per 1/4" wide, 50' long roll; if Lowes happens to be cheaper than that, it really doesn't matter, because at such low prices I'd rather have the specific technical specs, varied selection, single source, etc. supplied by McMaster; when you put all those features together, McMaster usually ends up being cheaper due to effort/time saved.)