Another "How to make" question

[whateg0]

I sent you a PM.

[Glenn Brooks]

Always the possibility of turning the round parts out of wood, then milling and cutting the spikes to length and gluing the pattern together. There are some videos on You tube of pattern makers explaining their craft. Always wanted to take on learning this, but it still remains some what mystical to me.

Glenn

[Mr Ron]

Always the possibility of turning the round parts out of wood, then milling and cutting the spikes to length and gluing the pattern together. There are some videos on You tube of pattern makers explaining their craft. Always wanted to take on learning this, but it still remains some what mystical to me.

Glenn

Good idea! I will investigate to see if I can learn to do it.

[pete]

Maybe pointless information since I've never worked with that type of resin before Ron. With the added weight of the loco sitting on them I'd be a bit leery of those resin castings moving a bit over time I think. You did say it's mostly for display so painted rims will never replicate the color of steel properly. Maybe making the outer diameter of the castings slightly smaller and bonding some steel rims on would both keep the round shape and duplicate what would have been done on the full scale one's anyway?

What rotary table do you have? Some like the Vertex have a dividing plate attachment available that's a big help in getting the proper degree settings unless it's an oddball prime number. I do know very little about locomotives, but if those spokes are the usual elliptical shape that's going to complicate the pattern a bit. Apparently 3D printable wax is available that's meant for patterns using the lost wax investment casting method. Casting the wheels in resin or metal might have little difference in time and costs?

[RSG]

The problem with using a RT is the angles are 7.4° and 14.8°. I can't accurately dial in those angles with my RT. I can only set it at 1° increments. To use a RT, I would have to "eyeball" the cutter path. I did make some wheels for another loco and used epoxy resin in a rubber mold. Those came out perfect with no further machining required; a little flash but that was all. If I wanted, I could machine a band and press fit it unto the resin wheel. That epoxy resin is very strong.

Can you not round up a bit to an even number? Then cheat a bit by raising the bottom plunge holes of the spoke to accommodate the difference? I know you want to try to keep the wheels to scale but they'd be out such a minor amount you'd never see it.

[RSG]

I took a few minutes to map it out for you. It's quite simple really and would take no time to do. The diagram below so close to your required spec you will not even notice.

[GlennW]

It's the same as what Ron had originally.

The difference is that Ron had just figured the tool path incorrectly, which is most likely why he stated the other time he tried something similar it didn't work out.

Ron,

You are trying to calculate the tool path from the center of the wheel to the edge of the spoke at the rim, which is why you are getting odd angles.

You need to offset the rotary table by half the width of the spoke plus half the diameter of the end mill from the center point of the wheel. You would then only cut all of the spokes on the side you offset to. (If you offset to the right, cut the right side of all of the spokes) Then you would start back at zero and offset to the other side of the spoke and go around and cut all of them. (Offset to the left and cut the left side of all of the spokes) Then you would go back to the start again and make each cut between the spokes using the rotary table. At that point, you could pretty much eyeball the start and stop point of the cuts.

I suck at explaining things, which is why I haven't joined in, so i hope you can understand what I am trying to describe.

Had I seen a larger drawing, I might have been able to pick up on the error earlier.

I know that RSG is quite proficient with a rotary table, so possibly he may give a better, more understandable description than mine!

[RSG]

Pretty much how Glenn described it but my method starts with cutting the outer radius first.

Assuming you don't need to do a finishing pass the steps below outline exactly how I do it. If you need to do a final pass the account for it with a .010" offset.

1. Dial part in on rotab
2. Move y - 1.46" leaving X at zero
3. Plunge all .25" dia holes around part as numbered starting at 6, 18....and so on
4. Connect the holes using the same di end mill.
5. Move Y to .598", using .125" dia end mill plunge all holes as numbered - 12, 36.....and so on
6. While using the .125" E/M offset the rotab X - .205" under the mill and connect the holes
7. Rotate the rotab 12 degrees for each slot and continue until you are done that side. Then shift the table .205" to the other side and repeat .

Edit - I should note the when milling the slots in step seven the degrees won't line up with the original numbers used to plunge the inner holes but once you land on one that works you simply add 12 degrees to it then continue from there.

[GlennW]

Ron,

The angles are not as you are saying.

The spokes are on 24 degree centers.

The pink lines are the center of the tool path of a 1/8" diameter end mill.

Using a 1/8" end mill you would start with the RT at zero with the spindle zero'ed over the axis of the RT.

Move the X axis of the mill over .125".

Move the Y axis .652" and plunge into the wheel.

Cut a slot by moving the Y axis to 1.549.

Move the Y axis back to .652"

Rotate the table 24 degrees and then do as above again.

Once you have all of the spokes cut on that side, go back to zero degrees with the RT and move the X and Y axes back to zero.

Now move the X axis in the opposite direction and do the same as before with the Y axis.

You will now have .125" wide spokes.

Once you get that figured out, the next step is easy!

[GlennW]

Once you have made it that far, the next step is to move Y back to 1.549" and connect the slots using the rotary table. (Pink line again)

Of course, there are short cuts, but this is one basic explicit way to demonstrate the concept of rotary table use.

Naturally, roughing and finishing cuts are also desirable, but i don't want to have to write a book explaining that step by step...

[Mr Ron]

RSG: Thanks! You have laid it out in a way for a knucklehead like me to understand. I was really thinking along the same lines, but maybe age has gotten the best of me. Sometimes one can't see the forest for the trees.

Pete: the locomotives I build don't weigh all that much. The cabs are made of wood; only the frame and running gear is of metal. A 3/4 scale engine might weigh around 10-15 lbs. I don't intent to ride these engines, but they will be powered to run on their own.

I realize there are places where things can be made, but that goes against the whole idea of making it yourself which is the goal of the "home machinist". I have always been a "do-it-yourself" kind of guy. I like to be able to declare "I did it all by myself" which usually results in gasps of wonderment and disbelief (good for the ego). When someone asks me why do I make it when I could buy it, my reply is "because I can".

[tornitore45]

What is the limitation that sets your RT resolution to 1 degree? Never heard of a RT like that.
Perhaps removing such limitation is the answer to endless filing.