CMT Ursus 250 Repair: 3) Carriage Hand Wheel

RobinHood

Ultra Member
Premium Member
#1
The hand wheel on the carriage was broken. I tried really hard to repair it, but without success. The material is White Cast Iron. It is considered non-weldable, non-brazeable because of its chemical composition (high chromium content). CMT uses this material extensively on hand wheels and dials as you can highly polish the surface or media blast it to give a nice soft satin finish. It also grinds very well - dial bearing surfaces are all cylindrically ground the lathe.

The wheel is in one piece now, but the aluminum bronze weld did not bond with the WCI as the surface does not wet. The reason it is staying together is because of the weld prep. There is no structural strength whatsoever.

Front view of wheel
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And the back side
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I don’t have any ductile iron stock big enough (8+” diameter), but I did find some 4330 of suitable size. Here the Carolina saw is slicing a 3+” wide disc off the log. I had it set for the slowest speed and light down feed. Took 90 min to get through. Neither the blade nor the log got appreciably warm - exactly what I wanted. This stuff can work harden pretty easily.

The 8.5” x 3.25” disc weighed just over 52 lbs. I’ll weigh the wheel once it is done.

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Here we are roughing out the front.
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And done. The OE is beside the billet for comparison. I am leaving the contouring of the hand portion to the end. I like to have flat faces for easier mounting to the rotary table to cut the two spokes. The sharpie marks roughly show what needs to be removed off the rim and what stays on the front.
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And here is the back roughed out on the lathe. The OE center hub was cylindrically ground inside to fit on the shaft as well as the outside to accept the travel dial. I will probably use the tool post grinder to finish off these surfaces - not 100% certain yet, as 4330 turns really nice with carbide tooling. I may just go with turned surfaces.
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More to come…
 

RobinHood

Ultra Member
Premium Member
#2
I did not grind the ID and OD with the TPG. Fine tuned speeds and feeds a bit more to get even better surface finishes and just turned the OD journal and the ID bore. Here it Is on the apron for a first fit-up.
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Next I mounted the wheel to the 12” BP rotary table to start working on the two spokes. Started with the 4 “corners”. The radius of the OE’s spokes - to - circumference is just over 24mm. The location of the Center of the circle was determined by using geometry. I set the Y-offset on the mill table and the angle on the RT. As mentioned elsewhere, this RT can accurately divide the circle into degrees, minutes and seconds. Since the bulk of the inside of the hand wheel was removed on the lathe, I had to use an center cutting end mill to locate the corner circle because of the step (You can see it in the picture). Plunged a 1/2” carbide EM through first, followed by a 3/4” one. Then switched to the boring head to open the hole to dimension.
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After milling the excess off the inside circumference and “stitch drilling” the roughed out wheel spokes look like this. I had previously machined the counter balance weight (6 o’clock position on the wheel) and drilled & tapped the handle mounting hole (12 o’clock position)

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There is still a little extra material to come off the inside to blend into the corner rounds. In the picture above you can see that they don’t quite match yet.

The OE wheel has a circular cross section of the perimeter surface - both inside and out. The outside I can turn on the lathe with a form tool.

The inside is another story. It can’t be turned on the lathe because of the counterweight and the handle boss. I think I am going to move the RT onto the Deckel KF2 3D pantograph and see if I can do some contour milling using a ball nose end mill.

Stay tuned for that…
 

RobinHood

Ultra Member
Premium Member
#4
Yes, that is an option.

I have to check, but I don’t think I have one big enough. IIRC, the largest one in my stash is 1/2”. The nominal diameter is 26mm. Plus, I only have imperial corner rounding end mills.