Axle Reamer

[mmagliaro]

I have had success at this using a "bearing burr", like the ones used for diamond-setting.
These do cut, but they also tend to polish the surface of the cone-shaped hole.
I only knew about them because my grandfather was a jewelry maker and diamond setter, so I
have some of his tools.  And one day, needing to deepen an axle cone that was binding, I saw
this and tried it.  I did not use it in a motor tool.  I just held it in a pin vise and used it by hand.

https://www.pfingstco.com/products/busch-steel-burs/446/

[peteski]

That bit appears to have way too shallow of an angle.  Axle cups have an angle of around 60 degrees.

[robert3985]

That bit appears to have way too shallow of an angle.  Axle cups have an angle of around 60 degrees.

@peteski - Peter, I'm getting set to produce four different types of caboose truck sideframes for 3D printing since my previous suppliers have all quit making them due to the collapse of Shapeways, and I've been thinking about how the pointy axle ends should be ideally positioned in relation to the axle cups as well as how deep the cups should be.  Do you happen to have some "best practice" information about that?

If so, I'd appreciate the information, and maybe others would also benefit from it.

Cheerio!
Bob Gilmore

[mmagliaro]

That bit appears to have way too shallow of an angle.  Axle cups have an angle of around 60 degrees.

I use one that is smaller in diameter than the original axle cup, so it does get down into the bottom of the hole.
I really am only opening up a a little clearance right at the point at the bottom. The rest of the cone walls aren't touched.

[peteski]

@peteski - Peter, I'm getting set to produce four different types of caboose truck sideframes for 3D printing since my previous suppliers have all quit making them due to the collapse of Shapeways, and I've been thinking about how the pointy axle ends should be ideally positioned in relation to the axle cups as well as how deep the cups should be.  Do you happen to have some "best practice" information about that?

If so, I'd appreciate the information, and maybe others would also benefit from it.

Cheerio!
Bob Gilmore

No, sorry Bob.  My info is based on observations and attempts to measure the axle point's angle.  I don't even know if the model manufacturers follow some best practice or they are just "winging" it.

I believe that @Lemosteam and @Chris333 both designed and 3D printed N scale truck sideframes.  Maybe they will have more concrete information.

[Chris333]

These are HOn30, but use 36" ESM N scale wheels
https://www.printables.com/model/528906-maine-truck-hon30
https://www.printables.com/model/528914-hon30-jackson-and-sharp-type-trucks
https://www.printables.com/model/859963-hon30-gilpin-ore-cars
https://www.printables.com/model/682414-hon30-logcar
These take the same wheels, but have a little notch to help the axles in:
https://www.printables.com/model/913753-new-lime-rock-dump-car-hon30
https://www.printables.com/model/882150-eureka-mill-ore-car-hon30

As for the point to point distance. It is more than the length of the axles. I did it the same length and they were tight. Kept going wider till the wheels popped right in a spun out of the printer. All of my HOn30 trucks are printed.

I know another modeler who puts a tiny round ball at the end of the point to lessen it getting filled with resin.

I've not had to ream or drill mine out, but I have done that with Shapeways trucks.

I'm pretty sure they are drawn with a greater degree than the axle points.

[Maletrain]

I remember seeing some drawings somewhere.  The cup angle was about 10 degrees wider than the axle point angle.  And, ESM wheel set axles points are about 10 degree narrower than the other wheel set axle points, so about 20 degrees narrower than the pockets.

My experience is that the wheel set axle lengths are shorter than the pockets, which would mean that the points are actually riding on the upper surfaces of the conical axle pockets, rather than the whole axle cone riding on the whole pocket upper surface.

I am still wondering if that won't eventually cause enough wear on the pocket surface to have the axle points ride in some sort of form-fitting depression in the upper pocket surface.  If so, I would expect rolling friction to increase.

ESM wheel sets are the freest rolling that I have used, but I do not have enough actual rolling time on them to draw any conclusions about wear on the pockets. 

Maybe Bryab Bussey can enlighten us.

[peteski]

I am still wondering if that won't eventually cause enough wear on the pocket surface to have the axle points ride in some sort of form-fitting depression in the upper pocket surface.  If so, I would expect rolling friction to increase.

Maybe Bryab Bussey can enlighten us.

Wear of the bearing cups does occur (at least in Kato locos in maintained high-mileage examples).



Notice that (like you mentioned) the wear is towards the top of the cup and likely in the direction the loco traveled the most which seems to indicate that the cups cone angle is wider than the axle point.

I  suspect that since rolling stock is much lighter and the wheels are not driven, such severe wear is unlikely to occur.

Good point about Bryan since he was likely involved in ESM's wheelset design.  Calling @bbussey

[Lemosteam]

All of my home printed and Shapeways trucks used a 70 degree included angle pocket with a spherical bottom. I use a set like this one to clear out the pocket at the bottom and to smooth it.  These will also work in injection molded trucks.

My designs use a lead in groove to avoid over stressing the sideframe and to allow the axle point a guide into the pocket.

Having a spherical bottom pocket allows the axle point to ride a single point contact by design for minimal friction (the real secret). The axles really ride on a single point contact at the top of the cone in the truck (at least before they wear through the electric point pickup cups as in Pete's images, lol, then they have a line contact).

I ran a 5 day torture test of printed trucks under vertical an side loads without a failure and the truck rode as smoothly as any other truck on the market after I pulled it off the test fixture.

The metal axle on resin is ideal, although delrin on delrin is a little better due to the natural lubricative nature of the polymer.

Regardless I feel the ball point really works well for this purpose.  I suppose one could make a double ended ball reamer at various lengths to accomplish the same goal as the OP's title.

[robert3985]

Thanks to all who have responded to my request!  This gives me a direction to go in designing the actual mechanics of my trucks instead of just milling about smartly before sitting down and drawing the models. 

Cheerio!
Bob Gilmore

[peteski]

All of my home printed and Shapeways trucks used a 70 degree included angle pocket with a spherical bottom. I use a set like this one to clear out the pocket at the bottom and to smooth it.  These will also work in injection molded trucks.

My designs use a lead in groove to avoid over stressing the sideframe and to allow the axle point a guide into the pocket.

The lead-in groove is a very smart design which is used by many model RR manufacturers (I often see it in European models).

As for the spherical bottom, in my observations all the axle cup bearings have some sort of spherical bottom, and I suspect that like in your design the angle of the pointed axle is slightly different than the included angle of the bearing cup. The axle length is also slightly smaller than the distance between the axle cup bottoms. That results in a single point of contact on each side and also allows the axle to self-center in the truck.

[Lemosteam]

I design the bottom of the cup of the spheres on each frame to be exactly the axle length specified, knowing I will grind some out for the best rolling characteristics.

@robert3985 , if your cad tool has Boolean operations capability, I have a solid of the bearing cup that can be placed where you want it on the journal center and at the depth into the sideframe that provides the axle length, then you remove the solid from yours and you are left with the pocket.

Reach out to me if you feel it will help.