Attaching Parts Not Meant To Go Together

pebbleworm

pebbleworm

Active User
Registered
Joined
Jan 10, 2013
Messages
176
I've finally gotten around to installing a degree wheel and index plate on my Unimat to use it as a light duty spindex, mostly for laying out model parts. The degree wheel was originally part of an animation stand and will fit on the Uniomat pulley, but there is not a lot of material to tap into. I have the center of the blue plate reamed to the bore diameter of the pulley and it is now nicely centered, but the center will have to be bored out to clear the pulley nut. My problem is how to attach the index plate to the pulley- you can see the face of the plate is almost all index holes and there is only a thin rim at the edge where there is metal to drill into. My current thought is to keep the parts centered and drill holes for small diameter roll pins around the rim, then bore out the center for clearance for the nut and pin the parts in place, probably with some adhesive as well. This is a Unimat, so there is not going to be a lot of stress on these parts. This will leave the plate with minimal to no support at the center of the pulley which I don't like in theory, but again there is not a lot of stress on these parts. I could fill the recess in the face of the pully with epoxy putty but I think that would only make me feel better. Does this seem like a valid approach, or does anyone have any better suggestions? I am trying to keep the process simple.

Pulley and plate.JPG pulley and plate apart.JPG pulley spindle and plate.JPG
 
If it were mine, I'd probably drill and ream a couple or more holes through the degree wheel into the boss in the centre of the pulley for 3/32" or 1/8" roll or dowel pins, then clamp the degree wheel down with the pulley nut and a sturdy washer to prevent galling - positive location of the degree wheel that'll take a reasonable amount of torque. If you're concerned about excessive force breaking something else along the chain, use soft alloy/copper/brass as a sacrificial shear pin?
If there's clearance between the boss and the back of the degree wheel add a soft washer (copper or ally?) between to take up the gap so the wheel's not deformed when you tighten the nut onto it, before drilling and reaming and inserting the pins (you may need to make a "spud" to hold all aligned for the drill/ream/pin operations).
If you're thinking the degree wheel will be a permanent fixture, you could substitute countersunk machine screws for the pins, but would (unless they were brass) lose the shear pin safety....

Dave H. (the other one)
 
Why are you going to bore a clearance hole for the nut? It appears that the shaft extends far enough through the assembly to install the nut. If the nut bearing surface on the pulley is below the surface of the rim, you can use shim washers to bring the surface to the same plane. If it were me, I would try to keep the registration that you now have. Three or so strategically place dowel pins on the rim should give you a stable index plate.
 
Glue it to the shaft with some blue Loctite used for screws, so that way if you needed to take it apart, you could do so.

BTW-Your bearing may be damaged. The outer race should have not removed itself from the inner. The outer race may have burnish marks from the steel balls skidding sideways in the race when it came apart.
 
Thanks! Once the spindle is installed on the lathe there are not enough threads for the nut and the index plate. The pulley boss and rim are flush so a washer would not help support the index plate (unless I cut a recess in the back of the index plate. Hmm...). That is why I was thinking of filling the recess with epoxy, even though a 3" diameter piece of 1/4" aluminum should be OK if only supported at the rim. I am thinking of using roll pins because there is only 4mm band of overlap on the pulley rim. And yes, the bearings are shot!

headstock pulley.JPG
 
Ah, OK, the third pic is a little deceptive! Machine a little out of the centre of the degree wheel, leaving a recess for the nut to sit in? 1/8" or so thickness under the nut should be enough to secure it - probably be best to use small countersunk screws into the boss rather than roll pins etc. I think roll pins / etc. at the rim might prove more problematic as you'd run the risk of them protruding into the pulley groove, not nice for the belt!
Is there no key between the pulley and the spindle? You'd need to ensure that the two couldn't rotate independently or you'd lose registration for indexing...

A completely different idea, could the degree wheel fit on a mandrel to slip inside the spindle and expand with a centre bolt? It's difficult to know sizes, I'm used to somewhat larger machines!

Dave H. (the other one)
 
You must log in or register to reply here.
Back
Top