Scratchbuilding locomotive drivers

[Hawk]

I am in the process of learning myself to scratchbuild locomotive drivers in 0-scale, and hopefully this is a subject that might be of interest to others.  But at the time of writing I have not finished a single wheelset, so it is going to be quite a lot of trial and error in this thread!

 

The concept is modelling wheel centers n Fusion360, 3D printing masters and finally having them cast in brass. Tyres will be machined in mild steel.

 

What I have achived so far is machining tyres for two electric engines of this type:

 

 

Here is a little photo-essay on how I made the tyres.

 

My lathe is a Wabeco D4000, a machine that despite its quite hefty price tag has gotten somewhat mixed reviews.  My impression is that the machine is more than adequate for work in 0-scale, and the troubles I have encountered is certainly more due to my experience than the qualities of the machine. 

 

But enough with the disclaimers, here is how I did it. 

 

1. A piece of mild steel with a diameter around 1mm larger than the larges diameter on the finished tire is chucked firmly into a regular 3 jaw chuck. As all operations is done without re-chucking, a ordinary chuck is good enough. Purists will probably shake their heads already, the bolt extrudes far more than recommended. But I am a lazy bum, so I wanted to see if I could machine 8 rims in one setting. reducing this to 4 is probably wise:

 

2. The end is faced off:

 

3. The bolt is bored with a center drill:

 

4. The live center is placed firmly in the hole:

 

5. The carbide tool is set exactly to centre height. This is critical for a good result. I am measuring against the live centre in the tailstock:

 

6. Turning the bolt to a diameter slightly larger than the finished wheel:

 

7. With a parting tool slots are machined into the bolt. This defines the width of the tires, and are also an important relief for the profile tool used in the next step. Extreme care is neccesary for this and the next operations. Steady, slow feed and low rpm (around 50-100RPM) is essential. I lubricate with WD-40, wich probably is not the best lubricant, but it seems to help:

 

8. With a form tool from Protocraft in the US the final profile is machined. Now even more care is needed, i run my lathe as slow as possible. (50 RPM). Again, steady feed is a must. I lock all slides except the cross_slide. Note that the overhang of the tool is as small as possible. I did also add custom-made packings for critical spots on the tool holder:

 

9. For the next operation, the live center is removed, and the inner hole drilled with successively larger drills. If you look closely you can see that I ruined my largest drill:

 

10. The final size of an inner bore should always be made with a boring tool and not a drill. My $ 8 boring bar from eBay was just fine for the job:

 

11. Chamfering the edge of the tires:

 

12. The moment of truth. Parting off the tires. Easy does it!

 

13. At last, success! 

 

14. Dial caliper beside the tires to show the size of the wheels. The outer diameter is 22mm.

 

14. All the different lathe tools used. A quick change tool holder is a must in my opinion:

Well, thats all for now. In a not too distant future I will sho how I machine cast brass centers and assemble the wheel sets. 

Thanks for reading this far, and keep the comments coming! All suggestions and criticism is welcome.

 

Best regards, Håvard H

 

Edited August 11, 2023 by Hawk

[Booking Hall]

Thank you for this very informative 'how to', I look forward to future instalments!

[Guest Isambarduk]

Very interesting work, Hauk.  I shall follow with much interest.

 

I have made a good number of 0 gauge steel tyres over the years, pretty much along your lines. Some of them were destined to go on cast iron wheels, others on plastic or brass.  I have made the pattern for casting the latter, eg

 

More captioned images at: www.davidlosmith.co.uk/Andrew-Barclay-Fireless.htm

 

or just machined up a set, eg

 

More captioned images at: www.davidlosmith.co.uk/LMS_Fowler.htm

 

 

David

[Hawk]

Very interesting work, Hauk.  I shall follow with much interest.

 

I have made a good number of 0 gauge steel tyres over the years, pretty much along your lines. Some of them were destined to go on cast iron wheels, others on plastic or brass.  I have made the pattern for casting the latter

Some very fine models you have got there, David!

 

May I ask where you put the insulation on your wheels? And what do you use for the insulation?

[Guest Isambarduk]

May I ask where you put the insulation on your wheels? And what do you use for the insulation?

 

Typically, I put the insulation between the rim and the wheel centre; I use a thin (0.25mm) sliver of acrylic.  I machine the wheel centre so that the tyre is a good press fit but I also put epoxy resin on the inside of the tyre and outside of the wheel centre before I press the tyre on.  When the epoxy resin is set, I clean up any excess and I machine the final profile on the tyre.  Clearly, if I am using a plastic wheel centre, I need only to turn it so that the tyre is a good push fit, again with epoxy resin in the join; in this case, I usually turn the tyre profile beforehand and then try my best to ensure that the tyre runs true on the wheel centre, adjusting if necessary.

 

As it happens, the two examples that I illustrated have split-axle pick-up so the steel tyres were just pressed on the brass wheel centres and the insulation is at the split axles.

 

David

[Hawk]

As mentioned in the last post, the plan is to have the wheel centers cast in brass.
I need only castings for two engines, and it is almost as cheap to have them all printed by Shapeways instead of having them cast by a casting service. (The cost for one wheel centre excluding postage was € 13.45) But I have a small hope of getting some other modellers interested in modeling my favorite railway, and then it would be nice to be able to offer some castings for sale.

I have made the digital master for the 3D-print in Fusion360, and even if all the fillets and the form of the spokes is not perfect, I think no one will notice on a wheel less than an inch in diameter (22mm to be precise):




A test was printed with Shapeways, and even if the surface is quite rough, I think it is passable for cast iron. But I think I will try and send the pictures to a casting service to hear if they can achieve a somewhat smoother surface:

 

 

What do you think? Is the surface finish good enough?
More troubling than the surface is the shrinkage of the part. The digital model has an outer diameter of 20.18mm, while the finished brass part is 19.8mm. Shapeways claim a shrinkage of around 1%, somewhat less than the almost 2% shrinkage I encountered. I also suspect that the part has been somewhat polished, even if I ordered a part in "raw brass".

 

The 5mm diameter stub on the back is for mounting the casting in a collet on the lathe. It will be interesting to see how well the cast brass will machine. Suggestions for type of tool, feed and speed are welcome!

 

Edited August 11, 2023 by Hawk

[JohnGi]

Very interesting and informative thread.

 

 

More troubling than the surface is the shrinkage of the part. The digital model has an outer diameter of 20.18mm, while the finished brass part is 19.8mm. Shapeways claim a shrinkage of around 1%, somewhat less than the almost 2% shrinkage I encountered. I also suspect that the part has been somewhat polished, even if I ordered a part in "raw brass"

 

 

Where did you get your figures? According to Shapeways website..

 

 

Your model may shrink about 0.15 mm plus 1.5% after casting and finishing.

For rings the inner diameter will be 0.125 - 0.15 mm smaller than your design. On average, the model shrinks about 1.5% after casting and finishing. Scaling up your model by 1% will make your design closer to your desired size.

 

Using their figures I calculated 19.7 mm for your finished wheel, pretty close to what you actually got.

 

 

 

Edited January 30, 2018 by JohnGi

[Hawk]

Very interesting and informative thread.

 

 

 

Where did you get your figures? According to Shapeways website..

 

Using their figures I calculated 19.7 mm for your finished wheel, pretty close to what you actually got.

I focused on the sentence "Scaling up your model by 1% will make your design closer to your desired size.". I thought that meant that shrinkage was 1%. It seems a bit counterintuitive that you should increase the size of the digital model 1% to compensate for a 1,5% shrinkage.

[sej]

Excellent stuff Hawk, very interesting and very clever!!

 

Cheers

Simon

[Bucoops]

I focused on the sentence "Scaling up your model by 1% will make your design closer to your desired size.". I thought that meant that shrinkage was 1%. It seems a bit counterintuitive that you should increase the size of the digital model 1% to compensate for a 1,5% shrinkage.

 

Percentages are weird

 

Add 10% to 10 and you get 11.

Take 10% from 11 and you get 9.9

[Hawk]

Percentages are weird

 

Add 10% to 10 and you get 11.

Take 10% from 11 and you get 9.9

 

 

You are right, I should have given the equation a bit more consideration.

 

Another matter while I am at the keyboard: I tried to machine the castings last night, and a carbide insert tool gave the absolutely worst surface I have ever managed to achive in my career as an amateur machinist. A home ground HSS toolbit worked far better. 

 

Is the poor finish to be expected using a carbide insert tool on cast brass, or is it a feed/speed issue?

[Hawk]

Excellent stuff Hawk, very interesting and very clever!!

 

Cheers

Simon

 

I will go along with "interesting",  but how clever it all is remains to be seen...

But hopefully there will be some pieces of useful information among all the noise!

[dajt]

It doesn't surprise me the HSS gave the better finish - I would have used HSS and high speed in this case. I only use carbide inserts for taking big cuts quickly, or where I don't care about surface finish.

 

Sharp HSS and fine cuts will probably put less load on the wheel too. Fine cuts with carbide might rub more than cut.

 

The only thing I question is what else is in the print, any binder left etc? That might make it sticky or something.

 

But I'm an amateur too so my opinion is worth what it cost

 

Thanks for posting though, very interesting.

[Hawk]

It doesn't surprise me the HSS gave the better finish - I would have used HSS and high speed in this case. I only use carbide inserts for taking big cuts quickly, or where I don't care about surface finish.

 

Sharp HSS and fine cuts will probably put less load on the wheel too. Fine cuts with carbide might rub more than cut.

 

The only thing I question is what else is in the print, any binder left etc? That might make it sticky or something.

 

But I'm an amateur too so my opinion is worth what it cost

 

Thanks for posting though, very interesting.

Thanks to all for the feedback!

 

It is important to remember that this "print" from Shapeways is not really a print at all. Shapeways prints a wax master and makes a regular lost-wax casting from it. So it´s properties should be like any other brass casting. That said, I have other castings that has machined better with carbide insert tools. But as I would really like to get as much tool grinding experience as possible, I will try to use HSS as much as possible for my lathe work.

[Guest Isambarduk]

 

What do you think? Is the surface finish good enough?

 

To be perfectly honest, I would have been rather disappointed at that, so I would go for making a pattern and lost wax brass castings.  David

Edited February 1, 2018 by Isambarduk

[Guest Isambarduk]

 

Is the poor finish to be expected using a carbide insert tool on cast brass, or is it a feed/speed issue?

 

Well, I use a carbide tool - I silver soldered a carbide chip onto a mild steel shank and ground it to shape - and it works very well on brass.  I generally take light cuts and relatively slow feeds on the final cut with my small lathe (Unimat 3) but the speed is not that critical, I find.    David

[flubrush]

It is important to remember that this "print" from Shapeways is not really a print at all. Shapeways prints a wax master and makes a regular lost-wax casting from it. So it´s properties should be like any other brass casting. That said, I have other castings that has machined better with carbide insert tools. But as I would really like to get as much tool grinding experience as possible, I will try to use HSS as much as possible for my lathe work.

 

Hawk,

 

We have lost wax brass loco wheel centres in the S Scale Parts department to be used in wheel making much as you are describing..  The comment I had from the person who originally commissioned the castings was that our supplier's castings don't provide the best detail available but the brass he uses was found to be the best for machining.  So it sounds as though there are a few types of casting brass in use,  some of which probably don't machine well.

 

Jim.

Edited February 1, 2018 by flubrush

[brianCAD]

 I tried to machine the castings last night, and a carbide insert tool gave the absolutely worst surface I have ever managed to achive in my career as an amateur machinist. A home ground HSS toolbit worked far better. 

 

Is the poor finish to be expected using a carbide insert tool on cast brass, or is it a feed/speed issue?

 

Håvard,

 

In a nutshell, use HSS for brass and for any fine finishing work in steel. 

 

> I am not entirely happy with the finish of the inside bore.

> I used a boring tool with carbide inserts ( 8 dollars on eBay...)

 

Reserve your (positive rake) carbide insert tooling for heavier cuts in steel. Ignore negative rake tools which require more power and rigidity than hobby sized machines possess.

 

HSS takes on a sharper edge than most carbide inserts provide - although a carbide tip can be reground to resemble the geometry of a HSS tool, its edge might soon crumble microscopically. 

The pointed tip of a HSS tool should not be left sharp.  The vertical edge, where the angled side and end faces meet, will benefit by having the tiniest radius applied.  A few wipes of an oil stone suffices - but take great care to maintain a positive rake cutting edge, and not round off any of the tool's horizontal edges.

 

Until about two years ago, I was using Shapeways to provide large numbers of assorted driving wheel centres as brass castings.  These came from their New York base and my experience from there differs to yours.  The castings were always a very close match to the CAD file size, varying only by two or three thou in diameter on wheels typically of about 1inch in diameter.  On one occasion the castings were one thou larger than the CAD, so I assumed any scaling necessary for the casting process was accommodated by one of their automated processes.

 

The waxes were made with the wheels standing upright (presumably to maximise part count on the machine platen).  This meant that the spokes close to vertical alignment showed no 'stepping', but those spokes extending out close to horizontal alignment had ever increasing evidence of 'fishtailed' stepping as they became nearer to horizontal.  On counting up these visible steps, the resolution sometimes seemed coarser than their claimed 16 micron layer thickness.  To avoid any cheating (if indeed it was occurring), I resorted to purchasing only the waxes (which I could inspect first) and then had them cast by other parties for a better result.

 

Shapeways (NY) always insisted on tumbling their brass castings which rounded off any desirable sharp edges (but not actually a problem for wheel castings with machining allowances built in).  One batch arrived 'polished' which damaged counterweights, but was quickly replaced by Shapeways.

 

Cheers, brianCAD 

[Hawk]

Håvard,

 

In a nutshell, use HSS for brass and for any fine finishing work in steel. 

 

> I am not entirely happy with the finish of the inside bore.

> I used a boring tool with carbide inserts ( 8 dollars on eBay...)

 

Reserve your (positive rake) carbide insert tooling for heavier cuts in steel. Ignore negative rake tools which require more power and rigidity than hobby sized machines possess.

 

HSS takes on a sharper edge than most carbide inserts provide - although a carbide tip can be reground to resemble the geometry of a HSS tool, its edge might soon crumble microscopically. 

The pointed tip of a HSS tool should not be left sharp.  The vertical edge, where the angled side and end faces meet, will benefit by having the tiniest radius applied.  A few wipes of an oil stone suffices - but take great care to maintain a positive rake cutting edge, and not round off any of the tool's horizontal edges.

 

Until about two years ago, I was using Shapeways to provide large numbers of assorted driving wheel centres as brass castings.  These came from their New York base and my experience from there differs to yours.  The castings were always a very close match to the CAD file size, varying only by two or three thou in diameter on wheels typically of about 1inch in diameter.  On one occasion the castings were one thou larger than the CAD, so I assumed any scaling necessary for the casting process was accommodated by one of their automated processes.

 

The waxes were made with the wheels standing upright (presumably to maximise part count on the machine platen).  This meant that the spokes close to vertical alignment showed no 'stepping', but those spokes extending out close to horizontal alignment had ever increasing evidence of 'fishtailed' stepping as they became nearer to horizontal.  On counting up these visible steps, the resolution sometimes seemed coarser than their claimed 16 micron layer thickness.  To avoid any cheating (if indeed it was occurring), I resorted to purchasing only the waxes (which I could inspect first) and then had them cast by other parties for a better result.

 

Shapeways (NY) always insisted on tumbling their brass castings which rounded off any desirable sharp edges (but not actually a problem for wheel castings with machining allowances built in).  One batch arrived 'polished' which damaged counterweights, but was quickly replaced by Shapeways.

 

Cheers, brianCAD

Thank you for an informative reply! If you have some pictures of your wheel projects, I would be very interested in seeing them.

[Guest Isambarduk]

If you have some pictures of your wheel projects, I would be very interested in seeing them.

 

I know that you weren't asking me, Hauk, but here is a photo that I took to illustrate what was up to when I was building my Andrew Barclay fireless loco and there were no proprietary wheels available at the time. 

 

 

On the left is the raw brass casting (cast by commercial casters in Birmingham from my brass pattern), moving to the right is a casting with the first machining operation performed (looking at the back of the wheel) and the next is the casting with all the machining operations completed.  Moving right and towards the back is a steel tyre and finally, on the far right, is a finished wheel with the tyre pressed on and a crankpin fitted.  As the model has split axle pick-up, there is no insulation at the wheels.

 

 

The wheels on the model

 

 

Andrew Barclay 0-4-0F  More details

 

 

David

Edited February 2, 2018 by Isambarduk

[Hawk]

I know that you weren't asking me, Hauk, but here is a photo that I took to illustrate what was up to when I was building my Andrew Barclay fireless loco and there were no proprietary wheels available at the time. 

I appreciate the input!

Is the crankpin press-fitted? And how did you hold the casting while machining?

 

 

As I am looking for a contract casting company, do you know if the Birmingham caster you used are still in business?

[JeffP]

Percentages are weird

 

Add 10% to 10 and you get 11.

Take 10% from 11 and you get 9.9

Takes me back to trying to teach how to find the price of an item ex-VAT, given that the stated price includes VAT at 17.5%, (Which it then was). Much fun was had.......

[Re6/6]

Butting in here...!

 

These are a few of the late Nigel Hunt turned and fly-cut (P4) loco wheels which were waiting for their rims.

 

Just thought that they might be of interest.

 

 

 

[Hawk]

Butting in here...!

 

These are a few of the late Nigel Hunt turned and fly-cut (P4) loco wheels which were waiting for their rims.

 

Just thought that they might be of interest.

Obviously, there are many ways to skin a cat! But I am glad I don´t have to mill all my spoked wheels on manual machines.

[Hawk]

I have now for the first time tried to add a tyre to a casting. The insulation is a thin-walled tube of delrin acetat. This type of plastic machines remarkably well, and it is easy to machine a tube with 0.3mm walls.

While the tube was still in the chuck, I pressed the casting into the tube. I made a rather tight bore, so it was possible to skim the outside of the tube before pressing on the tyre. The fit was slightly loose, so I fixed the tyre with super glue.

After the glue had dried, I placed the wheel in freshly machined soft jaws. With soft jaws I have been able to rechuck the wheel with a runout of 0,02mm sideways runout measured on the tyre. Axial runout measured on the tyre is very close to zero.

When you machine the soft jaws it is necessary to tighten the jaws on a steel ring or similar:

 

Finally, the axle hole is bored:

 

I was a bit concerned that the forces from the machining would break the tyre loose from the casting, but it worked out OK.

Edited August 11, 2023 by Hawk