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Any idea at what temperature the plastic in katotrack becomes somewhat moldable?

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Any idea at what temperature the plastic in katotrack becomes somewhat moldable?
Posted by CanadaDavid on Monday, April 17, 2023 9:30 PM

I'm adding a short section.  I'm getting ocd about the track laying (because when I wasn't, it didn't work).  The elevation changes- up a bit from a flat level, then the incline decreases to a flat level a few inches above.  Probably about a 1.5% slope.  I have it laid out, then I'm thinking- can I bend the bottom (start of the climb) piece of track just up a bit so the angle change just doesn't come at the track jointer.  Similarly at the top, can I bend the end down.  I'm sure its a thermoplastic.  Any suggestions for what I should set my oven to to soften, but not completely melt the plastic?

 

 

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Posted by dknelson on Tuesday, April 18, 2023 10:43 AM

I would agree that what are sometimes called "vertical easement curves" are a good idea and that avoiding a sharp angle is wise for smooth operation, avoiding derailments, and avoiding unplanned uncouplings.

If I was using regular flex track I would try to make sure that the vertical easement curve is somewhere in the middle of the flex track piece, not near an end, and let the natural bendability of the flextrack follow the vertical easement that I would create with my subroadbed.  I have not worked much with Kato unitrack and do not know how long the longest piece is, but I suspect there is some limited flexibility therev- again in the middle of a long piece.  Too close to an end and all you are doing is bending the track joint which is exactly what you don't want

I would not try to "pre-bend" track in an oven, or by holding the track over a pipe or other round object  - I think the bend needs to be tailored to and made at the site of the situation.  If the Kato track just does not bend enough I wonder if an incandescent light bulb placed near the point of wished-for bending would do the trick (one bend at a time most likely).   Even then I'd have a spray bottle of cold water near by to avoid a melt down which can happen surprisingly quickly

Obviously I have not tried this idea.  But all my instincts tell me not to try to "pre bend" and certainly not in an oven.  As photographers of plastic models can attest, the amount of heat a light bulb gives off can be impressive.

Dave Nelson 

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Posted by Doughless on Tuesday, April 18, 2023 11:01 AM

Rather than melting, I would cut kerfs into the bottom of the roadbed to release its tensioned straightness.  I would assume the track and ties will follow the roadbed bend as long as its gradual.  I would also use the center of the section rather than the end.

Appearance wise, filling in the kerfs with something should not be a problem.  Or let ballast cover them.

- Douglas

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Posted by doctorwayne on Tuesday, April 18, 2023 1:35 PM

CanadaDavid
....The elevation changes- up a bit from a flat level, then the incline decreases to a flat level a few inches above. Probably about a 1.5% slope. I have it laid out, then I'm thinking- can I bend the bottom (start of the climb) piece of track just up a bit so the angle change just doesn't come at the track jointer. Similarly at the top, can I bend the end down. I'm sure its a thermoplastic....

I'd avoid bending anything sharply up or down....depending on the material that you're using as the roadbed, some shim-stock would be useful under an upward curve, and a file or some heavy-duty sandpaper to transition back into level track.

On my layout, I used 3/4" plywood for sub-roadbed, cut into both straight strips and curved ones, then supported them with suitable risers to ease into upward and/or levelling-out requirements...in other words, don't start an upward (or downward) curve from the end (or beginning) of level roadbed...instead start the rise or descent using the same piece of roadbed.

In the photo below...

...the track is level from the locomotive on one track and the caboose on the other, all the way to the turnout in the foreground.
From the turnout, the track begins (rather unnoticeably) to descend, and continues downward though several "S" curves...

...and then two large horseshoe-type curves, one to the right...

...and then down a straightaway to lower curve to the left...

...then, at left, segues onto level ground...

...no lumps, no bumps, no derailments.

Wayne

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Posted by wjstix on Tuesday, April 18, 2023 2:43 PM

I would go the other way - use the inherent stiffness of the Kato Unitrack to extend a series of thin shims underneath the tracks leading into and out of the grade. Start by raising the first section from flat to say 1/16", then the next from 1/16" to 1/8". You can fill in with intermediate shims or just add mixed gray ballast to cover the open area. Kato track is so stiff that a piece can support a train by itself if it's properly supported at each end.

Stix
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Posted by dehusman on Tuesday, April 18, 2023 3:30 PM

My take would be that if you have to physically bend the Uni-track, your vertical curve is too sharp.  Unless you are making a coal unloading dock, the bends shouldn't be that sharp.  Plus the plastic might bend when heated but the rail won't.

 

Dave H. Painted side goes up. My website : wnbranch.com

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Posted by snjroy on Wednesday, April 19, 2023 6:00 AM

My vote goes for sawing a series of  cuts underneath the track/roadbed. Melting plastic into a desirable shape is never easy.

Simon 

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Posted by reasearchhound on Wednesday, April 19, 2023 9:48 AM

I suspect the temperature you should set your oven to is that which is just below where your ties start to melt off the rails.

Because of that, I too would go with cutting a series of kerfs.

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Posted by OldEngineman on Wednesday, April 19, 2023 9:45 PM

I believe Kato also sells packs of matching loose ballast, so if you use the "cut kerf" approach, you can "touch up" where the cuts are when everything is done.

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Posted by dehusman on Thursday, April 20, 2023 10:36 AM

Once again, if you have heat the ties or cut kerfs in the ballast section to physically bend the track section, the vertical curve is probably too sharp.  You risk creating more problems than you will solve.

Dave H. Painted side goes up. My website : wnbranch.com

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Posted by Doughless on Thursday, April 20, 2023 2:25 PM

dehusman

Once again, if you have heat the ties or cut kerfs in the ballast section to physically bend the track section, the vertical curve is probably too sharp.  You risk creating more problems than you will solve.

 

I think what OP is saying is that a verticle easement requires a some amount of verticle flex in the track and roadbed, or else  there isn't a verticle easement. 

Laying roadbed and track separately creates this easment, but the plastic roadbed attached to the ties and track acts like sort of a boxed beam that provides no verticle flex at all.  There has to a be little bit of relief in order to get the small amount of flex needed.

- Douglas

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Posted by wjstix on Thursday, April 20, 2023 2:46 PM

I agree 100%. Kato makes track sections up to 14" long. With just a low shim between them, you could make a very low grade approach of about 28". I would lay the track out and do some 'real world' tests to see if you can get something like that to work before you start to 'shake and bake' the track. 

Stix
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Posted by TrainzLuvr on Thursday, April 20, 2023 7:55 PM

KATO sells 3 foot long flex track without the roadbed, as well as appropriate cork to match their roadbed height.

I would go for that option above any others because there's no melting plastic involved (with possible toxic fumes released if ABS) or messing with cutting and filling the gaps of the roadbed.

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Posted by wjstix on Tuesday, April 25, 2023 8:51 AM

TrainzLuvr
KATO sells 3 foot long flex track without the roadbed, as well as appropriate cork to match their roadbed height.

Which brings us to something I guess should have been asked up front - which scale is the OP in? What you say is correct for N-scale Unitrack, but not for HO. 

In HO, the longest straight is 14.5". With a 1.5% grade, you'd start with one end of the track being 0" and the other about 1/4". If you took another straight and connected to the zero end, and put a 1/8" shim under the joint, your track would now go from 0" to 1/4" over about a 29" stretch. I can't imagine you'd have any trouble with that gradual a change at the start of a grade, and it would be much easier than trying to guesstimate how hot to cook Unitrack or slice it up so you could to bend it up enough without popping out the rail. 

Stix
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Posted by dehusman on Tuesday, April 25, 2023 9:39 AM

Since Kato track is used around the workd and has been in production for decades, I find it hard to believe that this is the first time somebody needed to form a grade.

As such I think that the Kato track can accommodate a change in grade without resorting to cutting or melting the roadbed.

Dave H. Painted side goes up. My website : wnbranch.com

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Posted by Overmod on Wednesday, April 26, 2023 8:50 AM

In my opinion, the vertical stiffness of the rails exceeds any effect of the plastic roadbed in the vertical plane -- certainly with regard to setting and checking vertical transition spiraling.

If you were doing 'top-down fixation' the rails will describe a very shallow vertical S-curve, with the change starting slow at top and bottom, curving to a straight section in the middle (so you don't have two opposite curves trying to meet at one spot).  This is just like practice for horizontal curve spiraling, but at a different scale.

If you can, use something like a Surform to cut away the 'top' edge of the grade transition, and use gentle shimming and glue to form the 'subgrade' on the low part.  Think of it just as a real railroad might.  The track will then follow the determined grade profile with minimal kerfing or other manipulation -- if done right, I'd think that the normal thinned-adhesive-caulk method of track installation would work nicely without nailing.

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Posted by OldEngineman on Wednesday, April 26, 2023 9:33 PM

Have a piece of HO Unitrack sitting here on the desk.

This stuff is stiff. Trying to "bend" it to simulate the bottom or top of a grade takes a good deal of force, and even then, it won't flex much. And you'll need some strong screws to keep it held down this way.

A series of kerfs cut into the roadbed -- I reckon perhaps 5-7 -- and it will bend much more easily.

I would not try to bend it using heat.

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Posted by wjstix on Monday, May 1, 2023 9:29 AM

CanadaDavid
Probably about a 1.5% slope.  I have it laid out, then I'm thinking- can I bend the bottom (start of the climb) piece of track just up a bit so the angle change just doesn't come at the track jointer.  Similarly at the top, can I bend the end down.

Have you actually tried running equipment on the track? I think you're creating a problem in your mind that doesn't exist in real life. With that gentle a grade, I don't think you're going to have trouble.  

Stix
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Posted by LouC on Tuesday, May 2, 2023 7:37 PM

I've used the Kato track for my most recent layout and am using sections of code 83 flex ( Atlas) for some yard work and branch work due to the limits on available switch and track options in HO. I found some good ideas for mixing the Atlas with Kato track on Youtube and have had no issues. You might want to consider using a section of flex track for your transitions. You will have to use regular rail joiners at the joints and cut away a bit of the track base to make things work, but this is not a big deal.

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