How to bore split pinion?

[Bloy2004]

What would be the best approach for boring the existing 3/8" ID pinion to 1/2" ID?
I got this gearhead on ebay knowing that I needed a 1/2" ID pinion to fit my motor. I called Bayside to find out the cost of purchasing just a pinion of 1/2" ID, as the model comes with either option. They said it would be around $100.00 !!! (just the pinion)!!!
So I would like to bore this pinion out.
I figured maybe inserting a spacer in the slit and tighening the socket screw before chucking would secure it and allow a clean bore/ream. Is this a good approach? What are the options?
According to Bayside, the pinion is case hardened.

There is the possibility of turning down the motor shaft....or making an extension shaft/adapter plate with 3/8" on that.

This gearhead will be ideal for my Y-axis.

Thanks ahead for ANY advice.

Bloy

[DareBee]

Your clamping idea is about right. You will need micrograin carbide or ceramic to bore it; they may be prone to chipping when they hit the split and you will need to bore it from both ends. But this can be done.
Could also ID or jig grind in the same manor.

[Amnz]

Would grinding off the hardened surface with a small toolpost mounted grinder be advisable if the case hardening depth isn't a lot? This might help the boring bits?

Amnz

[Bloy2004]

Hi,

Thanks for the confidence..at least I know it can be done.
By rechucking the pinion to bore from both ends, is this to prevent taper from the bore tool extending in? Or is there another reason?

Bloy

[Bloy2004]

Also, if the boring were stopped shy of the projected 1/2", would that grinder idea of Amnz be used to "cleanup" the final bore?

Bloy

[Bloy2004]

Originally Posted by DareBee Your clamping idea is about right. You will need micrograin carbide or ceramic to bore it; they may be prone to chipping when they hit the split and you will need to bore it from both ends. But this can be done. Could also ID or jig grind in the same manor.

Oh! I think I understand (maybe) why you suggest boring from both ends.... the "slice" through the pinion from the solid teeth portion and the split mounting portion would put too much stress on the "un-sliced" metal left that bonds the two halves together during the turning operation. Is this correct?

Bloy

[DareBee]

I may have misunderstood; I assumed that it was a straight through bore & you had to open the whole thing up. As well it was discussed to clamp it on a stub arbour using the built in clamping method; which would mean that you cant turn the portion of the ID where it is clamped without truning it around.
Do you get what I meant?

Having looked at your pictures more caefully again. I would clamp the ID on the proper shaft size & figure what the gap is in the split. Then I would remove from the shaft & make shim pack & insert it into the split leaving the bore clear and clmp the screw tight.
Then I would hold the gear in a 4 jaw chuck and indicate it dead true (<0.0005 TIR) concentric and parallel. Now you can bore the whole deal straight through in 1 setup (which is better anyway).
I would be inclined (as mentioned earlier) to bore with high-grade micrograin carbide. You will have to take it easy and sharpen it a lot.
Then if you find that you get into soft material I would ream with spiral flute (because is easier than boring to finish size).
If you go to ream make sure the ends are chamfered or counterbored so your reamer will not hit the hardened material.

Actually you may be surprised, this gear may be a lot softer than we are anticipating (in this discussion)

[Bloy2004]

okay, Thanks DareBee,
I think i'm going to "do it" from your last advice...I'll need to get a spiral reamer and I have a few boring tools with carbide tip but I don't know about that micrograin carbide. I'll get that too as I should have them anyway..... probably have over a $100 in added tooling before this is done
This whole process is going to be fun if I take it slow....first REAL precision lathe work I'll have attempted.

My only concern is that by taking off the case hardening (should it be extreme), that the pinion won't stand up to the new forces. I imagine the stock 1/2" is hardened as is. Let's hope its not that hard.

Thanks so much!

Bloy

[Bloy2004]

Note! I just took a carbide scriber to the end and easily put two scratches in it....this is encouraging! AND, upon further inspection, it appears that the 3/8 bore was done AFTER any heat treatment.....almost a "honed" appearance.

....Maybe the person at Bayside was trying to convince me that I should buy one when he warned that it was case hardened......we'll see...

Thanks again!

Bloy

[DareBee]

Originally Posted by Bloy2004 okay, Thanks DareBee, My only concern is that by taking off the case hardening (should it be extreme), that the pinion won't stand up to the new forces. Bloy

Case hardening is used mainly to reduce surface wear, denting, etc. It doesnt really do much for strength, your only real strength concern should be wall thickness.
I wouldn't worry should be no problem.
I do these kind of mods all the time.

[Swede]

There's a strong possibility that if the pinion is case hardened, they may have treated only the gear teeth. Case/surface hardening can be selective, meaning they can leave the bore alone, and work just the gear faces.

Good carbide will cut darn near anything, it seems. I'll never forget when I snapped a high-speed steel Sossner tap (good quality) in aluminum, and the only way I could get it out was to mill it out (plunge!) with a 1/4" carbide end mill. The end mill ate that HSS tap like it was mild steel. Amazing. So a decent carbide boring bar will have no problems.

Some last-minute thoughts... 3/8" to 1/2" is a fairly small boring bar. This diameter shank will flex, and the amount of deflection will be proportional to the depth of cut. What you will want to do is steaily diminish the depth of each pass and sneak up on the target. Make the final 2 or 3 passes with a 0.002" or 0.003" max outfeed. You can also occasionally repeat a pass without additional "outfeed" and see if more metal is removed. If you doubt your ability to bore to 0.5004" or whatever, the spiral reamer is a good choice. Give the reamer 0.005" or so to bite. Some reamers don't remove small amounts of metal well; in other words, if you bore to 0.001" shy and try the reamer, it may rub rather than cut. I'd also test the reamer in a scrap of carbon steel in a drill press or similar, and check the result. Not all reamers are created equal, and some, especially new ones, can cut a wee bit oversized, which for a precision fit like this, is unhappy to say the least.

Finally, I toss this out for lathe beginners, not you necessarily. Some might be tempted to chuck this pinion, drill it out 31/64", then ream. This is an almost guaranteed way to produce an eccentric (uncentered) bore. Especially when the bore is split, like this one!

Finally, $100 for a pinion is RIDICULOUS!!!!

[Amnz]

This is interesting....