Any pointers on drilling/tapping hole in steel pulley?

[fitzhugh]

I'm swapping the 3/4 greenie motor for a dc treadmill motor and controller. The shaft is .67 / 17mm so I got a keyed pulley for it, only the shaft is not keyed. I figure it is easier to drill and tap for a standard shopsmith size set screw and grind a flat on the shaft than grind or cut a keyway in the shaft.

I have the drill (size F - very close to 1/4) and tap. I've used a center punch to mark the spot.

Now, other than using some oil, do I want to do anything? Pilot hole(s)?

Oh, I did make a v block to clamp it. The rubber pad that came with my diamond sharpening stone is doing a good job of keeping the pulley from moving in it.

I have the speed reducer, but I *think* for this I want around 1000rpm.

I've drilled lots of steel, but almost always sheet metal and almost always poorly. This time it matters.

[JPG]

I'm swapping the 3/4 greenie motor for a dc treadmill motor and controller. The shaft is .67 / 17mm so I got a keyed pulley for it, only the shaft is not keyed. I figure it is easier to drill and tap for a standard shopsmith size set screw and grind a flat on the shaft than grind or cut a keyway in the shaft.

I have the drill (size F - very close to 1/4) and tap. I've used a center punch to mark the spot.

Now, other than using some oil, do I want to do anything? Pilot hole(s)?ABSOLUTELY Start small and increase several times in between

Oh, I did make a v block to clamp it. The rubber pad that came with my diamond sharpening stone is doing a good job of keeping the pulley from moving in it.

I have the speed reducer, but I *think* for this I want around 1000rpm.

I've drilled lots of steel, but almost always sheet metal and almost always poorly. This time it matters.

Drill press fer sure. A vise would be a really really good thing. Not sure how a v-block will help. I would clamp the pulley from the bore ends.
Once positioned, I would also clamp the vise to the table.

Oh and the tap, by hand only. Oil will help cutting both with the drills and the tap. Tap 90 degree advance, 180 degree backoff(chip breaker) then repeat as often as it takes to get through.

Good Luck!

[jsburger]

I agree with all of JPG's advice. Particularly starting with a pilot hole and the taping method.

However you have the wrong size bit to drill and tap a 1/4-20 threaded hole. That is what you want to do, right? The tap drill is always smaller than the designated size of the threaded hole. A letter F drill is 0.2570". That is a clear hole for a 1/4-20 fastener. The correct tap drill for a 1/4-20 threaded hole is a number 7 which is 0.20100"

[paulrussell]

F is the proper drill for a 5/16 tap.

[fitzhugh]

Great, thanks.

By v-block I really wasn't clear. I cut a thick scrap piece in a v to help clamp it to the table. Since I'm drilling into the side of a cylinder I plan on leaving the shopsmith in horizontal boring mode. The block and rubber sheet are part of the solution, though I haven't stuck it on the table to see just how it works out. I don't want it to move AT ALL. Been there before. Leads to swearing and blood.


Sorry, I wasn't clear. I'm using the same 5/16 18 set screw as on the standard arbor because I have extras around and don't want to introduce something new to confuse me. Knowing me, I decided to check. I drilled and tapped a piece of maple and the set screw fits, plus the tap cleaned up a somewhat ugly threaded hole in one arbor nicely.

What about putting the tap in the ss chuck and putting a faceplate or sanding disk on the left side to hand rotate it, and advance it with the quill? I'm thinking just to start it straight. I'll do the rest by hand so I can get a feel for what is happening. If the pulley is still clamped it should be hard to misalign.

Oh, and I'm drilling in a smaller diameter section of the pulley that extends out, just to be clear.

[JPG]

What about putting the tap in the ss chuck and putting a faceplate or sanding disk on the left side to hand rotate it, and advance it with the quill? I'm thinking just to start it straight. I'll do the rest by hand so I can get a feel for what is happening. If the pulley is still clamped it should be hard to misalign.

Oh, and I'm drilling in a smaller diameter section of the pulley that extends out, just to be clear.

Actually that that is an excellent way to complete the tapping as well. One of the more common errors is applying side forces while rotating the tap. That method eliminates that. A smaller face plate would be my choice. I have done this with only the drill chuck. When the tap is straight, less torque is required.

You be tapping into the 'hub'.

Also realize the tapping will exert much more torque than the drilling.

[fitzhugh]

Great, thanks for all the advice. I'm off to try it. Obviously I worry I'll screw this up since I've been finding errands to run and other ways to avoid doing it all day

[skou]

I just think I've finally found the thing that a Mark series
Shopsmith EXCELS at over the Model 10. Since I don't have
easy access to mounting a sanding disc or faceplate to my
ER's backside, the Mark would be VASTLY superior to what
I've got. I may try to find one.

Fitz, I'd most likely use the 6 inch faceplate, or (if I still
had it) an 8 inch sanding disc, minus the paper.

Drilling it is a no brainer, run it SLOW, and use cutting oil.

Tapping (taping is what you do to walls, gifts, or even
recording nasty phone calls) UNPLUG the Shopsmith,
mount the tap in the drill chuck, NOT using the square
end of the tap, and advance the quill, and apply a moderate
pressure to the advance, while starting the tap.

It wouldn't hurt to try drilling and tapping a piece of scrap
metal, before trying on a real piece, just to get the feel
of the work.

steve

[fitzhugh]

Thanks, it worked great. Took your advice and did a test, gave meve feel. It went very well, actually. Only hard parts were actually layout and alignment. Layout because I don't have a center finder and has to use my caliper to last it out. Should of just made a center finder. Alignment because I didn't leave enough room between headstock and table to increase drill bit sizes and I thought it was out of slignment. I noticed the bit deflecting a tiny amount when testing it without power. Got it lined up, then noticed the same issue with the next bit. This time I had moved nothing but swapped bits and moved the quill in and out so I was suspicious... Finally noticed it was just my cheap bits: the faces are not actually perfectly symmetrical. It deflects up? Rotate it 180 and it deflects down. Same when the chuck is left in same orientation and only the bit is turned. So... It wasn't an issue with SD accuracy or precision. I'll get some center bits someday.

In any case, it worked, of course. I was worried about aligning the tap since that is always mentioned as a potential problem. This way it was hard to screw up TAPPING

Yeah, usually I catch such errors. Well, at least I like to think so. Guess I can't know about the ones I fail to catch!


Thanks again,
Fitzhugh