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When is 'enough is enough'?

-missy-

Entry posted by -missy-

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Hello :)

 

One thing that I have is tenacity. I find it very hard to give up on something, especially when that thing is a challenge. Sometimes it works against me so much that I end up getting very frustrated with it and I will admit, loosing my temper.

 

My poor Peckett has been a victim of this, some of you know that the chassis has been rebuilt as a result of it bouncing off a door after a flight across my living room. Fortunately the chassis was salvageable afterwards and was rebuilt to working order. I use the word working order lightly as me being me I wasn't happy with the way it was working, some might be happy with the results but not me. The rear wheels were not concentric and the result was the engine had a slight wobble to it when it traveled along the track. This meant that I have now spent a full weekend on the chassis to try and correct it, the end result is what you see below...

 

blogentry-2065-0-24906900-1357509371.jpg

 

I have found that the problem lies with the 3D printed wheels. I dont know though, if its a result of the printing or the way I am assembling them but right now I have managed to get 2 wheels out of 6 I am happy with. As you can see from the photo there are a few which just did not survive the numerous assemblies and disassemblies which happened over the weekend but I am now looking to get some more wheels printed to try and get 4 that I am happy with.

 

This does raise a few questions though...

 

1. Is the fault with the way I am assembling them? If so then how can I change or things to solve that problem or tweak the design to aid assembly.

2. Are the wheel rims workable with the printed rims?

3. Is 3D printing in FUD upto the quality to print the wheel centers yet?

4. Would it be better to print the wheels without a central hole and add one after fitting the rims?

 

I do know though that it is possible to produce a working wheel using 3D printed centers, though its just not as reliable as I would have liked though right now. Having to scrap 4 to get 2 good wheels to me isnt really good enough. One thing for sure though is I am not giving up on this little engine but until I get some more FUD wheels from Shapeways through the post, its going to one side, something I would not normally do...

 

Missy :)

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-missy-

Me again again!

 

We should not lose sight of the fact that all 2mm Association driving wheels are conductive to avoid having to use pickups, leading to better running.

 

I am not convinced about this, I have heard some people say that and I have also heard plenty of others saying it doesnt make any difference, after all both Farish and Dapol have adopted insulated wheels in their design so it cannot be that bad. Please note though that these particular wheels are NOT intended as a replacement in any way to the current range of 2mmSA wheels, I am just testing it to see if it is another viable alternative. As Andy has mentioned I am part of a team looking into various manufacturing techniques to eventually replace the 2mmSA wheels with something a little more 'assembly friendly'.

 

 

One way to go in 2mm would be to have them made in brass by i.materialise. http://i.materialise.com/materials/brass It is more expensive and they don't like doing builds with multiple pieces, but it would give you something that has know qualities.

 

Unfortunately not but a nice idea. As well as the details Andy has posted above, another problem lies in the fact the minimum wall thickness is 1mm. Unfortunately I think the only thing that is 1mm is the width of the wheel, the rest being well under. I am sure that in time the technology will get better and printing such things in Brass will be possible but sadly not now.

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billbedford

Unfortunately not but a nice idea. As well as the details Andy has posted above, another problem lies in the fact the minimum wall thickness is 1mm. Unfortunately I think the only thing that is 1mm is the width of the wheel, the rest being well under. I am sure that in time the technology will get better and printing such things in Brass will be possible but sadly not now.

 

Minimum wall thickness is 0.5mm, minimum detail 0.3mm.

 

 

What is a show stopper is that they hand polish and gold plate everything, which makes the pieces all shiney but takes off the sharp edges.

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2mm Andy

Me again again!

 

As well as the details Andy has posted above, another problem lies in the fact the minimum wall thickness is 1mm. Unfortunately I think the only thing that is 1mm is the width of the wheel, the rest being well under.

 

Actually it's 0.5mm min wall thickness according to their website....

 

(and Bill beat me to it!)

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-missy-

OK, apologies but its still a little too thick for 2mm spoked wheels. I have bigger plans for using that!

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nick_bastable
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Flying 2mm as i recall your not the first to launch a troublesome engine .......... :jester:

 

keep on trying your work still inspires numptys like me  :senile:

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-missy-

That is true Nick. Its not that I have a terrible temper or anything, far from it really!

 

I guess I just beat myself up (so to speak) too much when things don't go as well as I want them to. Its not anyone elses fault but my own.

 

Im not some hormonal crazed lunatic, honest!

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skipepsi
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I feel that as made the wheel centres need to be checked on a jig, A simple one  would consist of two axles protruding at right angles from a plate at the base of one axle would be a concentric rim to check the wheel centre fit the other would be recessed to accept the wheel centre with rim fitted. Both axles could be tapered to reduce stress on the wheel centres.

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Kylestrome
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Hi Julia,

 

I can well understand your frustrations and I have also been known to do drastic things with models that didn't work ;o)

 

I would definitely go for option 4. Use a collet to hold the rim, or turn one for the job, and drill the axles holes. It's the only way you can eliminate the unknown variables.

 

Regards,

David

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Donw
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From what you say only 2 of the wheels you sucessfully produced were sufficiently concentric. This is in line with what I would expect. The must be some tolerance on the 3D printing and to produce a wheel centre for 2mm where the rim and centre are accurate to the required level is asking a lot. So I think you either have to mount the wheels onto a shaft (or mandrel) and very lightly skim the rim or fit the centres into a rim then drill for the shaft.

The first seems impractical as the plastic spokes would be under a lot of stress. The second is a bit better but would need a lot of care.

 

An alternative approach might be to turn the rim out of a disk retaining a centre held by two or three steel spokes and fit the remainder of the spokes from printed parts. This follows Tim Watson's approach for the Midland spinner. However it does take you back to the split axles.

 

Personally I think you have achieved a lot so far. If the wheel centres are pretty cheap you could work on a trail and error basis. If an assembled wheel is not conentric you could scrap it recover the tyre and fit a new centre. You would need a couple of sensitive dial gauges to check wobble and concentricity of each wheel before fitting it to a chassis. Doing this as a pair could be frustrating if every pair had one duff wheel so could you test each wheel on a mandrel first and still be confident it would be ok on the final axle?

 

Don

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-missy-

Last night I ordered some more wheel centers. I have now ordered some without a central hole for the axle along with some of the original design. Hopefully my lathe is upto the job and will be able to drill the holes concentrically (I havent had much luck with this previously, even with collet chucks). I will try out the wheels with the axle hole first though as thats the easiest solution!

 

Thank you everyone for the replies too.

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richbrummitt

To answer the question in the title I have no idea but I know the feeling and you seem to be there regularly. I can only sympathise.

 

Hopefully my lathe is upto the job and will be able to drill the holes concentrically (I havent had much luck with this previously, even with collet chucks). 

 

I presume you are using a centre drill? If not you should get one: ordinary twist drills won't start a hole in the centre of a workpiece. They will follow a hole once you've started it with the centre drill though. Another thing that might be worth a check if you haven't done it already is the alignment of the tailstock with the headstock. It shouldn't be out by much, if at all, but we're not talking about much here.

 

Although I've no experience of doing it I would expect to be drilling the hole after fitting the tyre for a good result, as others have said.

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-missy-

Much better to start with a wheel with a undersized bore and then open it out with a hand reamer on the lathe.

 

Yes, but if that hole is not concentric then the reamer will not make it concentric. Much better to start with no hole.

 

To answer the question in the title I have no idea but I know the feeling and you seem to be there regularly. I can only sympathise.

 

 

I presume you are using a centre drill?

 

Yes, I have a collection of them, I think the secret is to find one suitable small enough to be able to use all of the drill. The problem I have is trying to clamp on the taper bit of the wheel tread in the collet. Its not as easy as it seems to clamp something that is slightly tapered. I must try that method which was explained in the 2mmSA magazine a few issues ago.

 

Although I've no experience of doing it I would expect to be drilling the hole after fitting the tyre for a good result, as others have said.

 

I think that is probably the best method right now, I will definitely be experimenting when they arrive.

 

Thank you.

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billbedford

Yes, but if that hole is not concentric then the reamer will not make it concentric. Much better to start with no hole.

 

In all the wheels I've had printed I haven't had one that has not been concentric. This does assume that your original CAD has the bore concentric to the rim.

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-missy-

Hello Bill

 

This is the whole problem I am having! I cannot get the wheels to run concentric, as I mentioned in the entry I got 2 good wheels out of 6, the remainder were not concentric once the rims where fitted and pushed onto the axles.

 

Im not even going to answer the question about the CAD drawing bit!!

 

M :)

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-missy-

Never heard of it!

 

Is it any good?

 

I was trained to use Inventor so it was the sensible thing to use at home....

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billbedford

Never heard of it!

I thought you might say that

 

Is it any good?

 

Good enough to draw trains with, a bit limited if you want to draw organic shapes.

 

I was trained to use Inventor so it was the sensible thing to use at home....

 

Fair enough.

 

I presume then that your software has snaps to ensure that the drawing components are concentric?

I can't see any way that a drawing that has its components concentric will produce a print where parts are not concentric.

So we are left with stuff like Shapeway's old machines leaving cruft on one side of the wheels and it not being cleaned off evenly

 

Thought: Are the wheels that broke the ones that were eccentric?

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-missy-

Yes, the software has snaps, in fact I think its harder to draw things avoiding the snaps instead of using them.

 

I dont understand it either, the fact I got 2 good wheels shows that it is possible, as you say it might be the tolerance of the machines they are using maybe?

 

No, the wheels that broke are the ones that were not concentric, they broke mainly because of my persistence trying to fix them, trying out different ideas.

 

I have sent off for some more so I will take a closer look at them when they arrive although the others seemed fine too, at least this time I have a fall back option with the blank axle holes just in case the same happens again. Persistence hopefully does pay off!

 

Thank you for all your help and advice

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2mm Andy

It would be interesting to hear the views of Damien at "Twomm Locomotives" - as far as I know he is the one person who is currently selling 2mm scale wheels printed in FUD, but with square-ended axles that press into square holes in the wheel centres, so I guess he must have done some testing to arrive at a reliable design.

 

Andy

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richbrummitt

I haven't asked and therefore don't know how much Julia's eccentric wheels were out but is it possible that someone else would think them close enough to be acceptable? 

 

Edit: I've read this again and it doesn't read as intended. I did not want to imply that Julia is asking or demanding too much and that she should accept something less. I've tried hard to rewrite it to read as I would like and haven't succeeded. Sorry.

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queensquare
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I haven't asked and therefore don't know how much Julia's eccentric wheels were out but is it possible that someone else would think them close enough to be acceptable? 

 

I probably would!

 

Jerry

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Atso

Just as another line of thought, have you thought of having the wheels laser cut? I had some test pieces done awhile ago and they seemed very good and fine. Unfortunately I've never actually used them in anger - no available tyres in N gauge. However some of the German finescale modellers use the same method to upgrade Fleischmann stock examples of which can be found here: http://www.raw-nette.de/henk/Br65Deutsch.htm

 

Sorry if you've already seen this page but it might prove to be a more precise route.

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