Dual track bender

DGE-Railroad

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I've been playing around with a 3D printed dual rail bender as a technical exercise.

The design isn't mine. The credit for that must go to a great chap called Pierre Rouzeau. It's printed in PETG with 100% infill. That required a reduction in cooling, a 245c hotend and a high bed temperature to get decent bed adhesion and remove warping.

PETG is the strongest filament outside of the exotic (carbon/metal) stuff and given the cost of the hardware: about £30, it works well at a very cheap price.

Here are the components and the result of bending code 332 brass track.
Trying to achieve a tighter radius resulted in the bender jumping off the track - due I think to imperfect roller shimming on my part. I will investigate this and see if I can push it tighter. The bender itself isn't breaking a sweat (and more importantly, isn't breaking!)

20201031_150845.jpg

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PhilP

G Scale, 7/8th's, Electronics
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Could the 'jumping' also be trying to reduce the radius in too big steps?

Would extra, gentler, passes help, perhaps?

PhilP.
 
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Greg Elmassian

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I'd guess the design has some angles built in to compensate for the plastic flexing a bit, and those angles might need to be increased. Would be interested in how you are "shimming" without adding more flex.

Nice design with rollers for the railtops, rather than the nylon slider most use.

How small a radius are you trying to bend, and have you inspected the rails themselves to see if they are still straight, or have a bit of twist? Twist would also cause the bender to slip off.

Greg
 
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FatherMcD

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Building this one tool could almost justify the expense of a 3D printer! Not that I'm looking for a reason to buy one, mind you. Please keep us updated on your progress and perhaps a link to the original design of Pierre Rouzeau?
 
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DGE-Railroad

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Here's Pierres page with the link FatherMcD!
Track Bender

Agreed, its pretty much paid for itself when you consider the printer is around £180 and th it requires about £2 of filament.

I've also been designing some point actuator covers of my own,so it's earning its keep!
 

PhilP

G Scale, 7/8th's, Electronics
5 Jun 2013
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Just a thought, re rail-bending..

As you go tighter, you have been cutting the web between the sleepers on the outside, and removing some from between the sleepers on the inside, of the curves? :wondering:

PhilP
 
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DGE-Railroad

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PhilP, dialling in a large radius immediately definitely exacerbates the problem. As soon as the jumping started happening I dialled back the bend and increased it very gradually but it will now jump off the track at anything greater than the shown radius.

Looking closely at how the bender sits in the track, I can see the cause: there's no engagement of the horizontal bearing for the outside rail. Its possible the print has shrunk by a mm or so which is enough to cause it.

That coupled with the fact the horizontal rollers on the corners aren't flanged and aren't shimmed that low (as suggested by Greg) means they aren't positively engaged and ride off the top, causing the jump.

I think it can be fixed either with shimming (which I think will only mean the corner rollers interfere with the track chairs) or by using flanged rollers on the corners to engage with the lip on the top if the rail and prevent the lift.

All fixable, the big positive is that the print is strong enough to handle the forces being asked of it - it's a good design.
 

phils2um

Phil S
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Where did you get the roller bearings (especially the flanged ones) and what did they add to the overall cost?
 

DGE-Railroad

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I must admit, I did forget to cut the outer ties on the first attempt. Being Aristo track, I'd unscrewed them from the bottom of the rails a while before, then completely overlooked the tie-cutting which I usually do for the outer rail.
 

DGE-Railroad

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All the bearings were bought through ebay. The regular ones were £7.36 for eight, the flanged ones were £2.88 for the pair.
 

DGE-Railroad

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Here's a shot where I've tried to capture the clearance and positioning issue.

As you can see, the main outside roller (left in the photo) sits quite high on the rail-side which I think is allowing it to ride up and off.

I'm going to try a flanged bearing here to see if that helps without reprinting the main carriage

20201031_214846.jpg
 
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DGE-Railroad

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Flanged bearings on the corners was the answer it seems. Much better engagement against the rail and it bends track like butter!
20201105_090523.jpg
I took a couple of videos, one bending to something like an R1 curve and then to see how easy it was to straighten

Applying a bend

Straightening
 
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PhilP

G Scale, 7/8th's, Electronics
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Excellent!
Did you modify the print-file at all?

PhilP.
 
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dunnyrail

DOGS, Garden Railways, Steam Trains, Jive Dancing,
25 Oct 2009
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Flanged bearings on the corners was the answer it seems. Much better engagement against the rail and it bends track like butter!
View attachment 275846
I took a couple of videos, one bending to something like an R1 curve and then to see how easy it was to straighten

Applying a bend

Straightening
Great vids Darren, always joy to use a Track Bender in use and good that you demonstrated the straigtening ability which is equally important. This should be an object lesson to those that think bending rail over your legs will give a smooth and acceptable curve. No only a Track Bender will do this to perfection, well one of these or ready bought curves that probably go through a similar process. I am lucky to possess an early made Massoth one with Peco Rail rollers that was used quite a lot in my Garden construction. I may have said it before but you really ought to get these in the shops for Xmas.
 
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DGE-Railroad

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Excellent!
Did you modify the print-file at all?

PhilP.
Thanks Phil.

No, I didn't adjust anything on the print file. That was something I wanted to avoid. I'm finding my way around TinkerCAD but am still VERY much learning!!
 

Paul2727

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Watched the vids and was impressed.I'll defo want one of those if it makes it into production.
Makes old home made single rail one look like coprolite.
Paul.
 
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Rhinochugger

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27 Oct 2009
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Great vids Darren, always joy to use a Track Bender in use and good that you demonstrated the straigtening ability which is equally important. This should be an object lesson to those that think bending rail over your legs will give a smooth and acceptable curve. No only a Track Bender will do this to perfection, well one of these or ready bought curves that probably go through a similar process. I am lucky to possess an early made Massoth one with Peco Rail rollers that was used quite a lot in my Garden construction. I may have said it before but you really ought to get these in the shops for Xmas.
I have never bent rail over my legs :shake::shake:

Round my belly, yes, but not over my legs :mask::mask:
 
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