Bad surface finish 6x12 surface grinder spindle disassembly questions

[metric_taper]

I ordered 54mm seals today.
And changed the setup, no clearance under the spindle for a boring head with long reach bar.
I'm finding I need a chamfering tool bar for the boring head. I want to break the edge so press fitting the seal will be easier.
View attachment Angle plate setup.mp4

 

[metric_taper]

Anyone have suggestions for measuring down into a hole. I'm having problems with reliable snap gauge on this 8mm boss. Does not help that the cutter is in the way.
I've always wanted the set of inside micrometers that can go deep into a hole, but I'm not that wealthy.

 

[Flyinfool]

You could make up a go / nogo gauge on the lathe. For the one time use, it could be made of AL.

 

[metric_taper]

You could make up a go / nogo gauge on the lathe. For the one time use, it could be made of AL.

I was thinking to do that last night, and should have after the problems with snap gauge repeatability. This morning I remembered I have this set of cheap bore gauges (Imperial). I set the one up for this range, calibrated it with a micrometer to zero the dial indicator at 54mm. I'm 0.005" larger then 54mm per this method. I hope there is enough left for the press fit, else epoxy is my friend.

 

[metric_taper]

The seal showed up today. I got that pressed in using the ram on the vertical mill. Seems to be tight enough.
Next problem, I purchased an ER50 collet holder on eBay, with a Weldon shank (40mm). The description say's 0.0002" TIR. I'm reading 0.0027 TIR without a collet. I'm using my zero set Bison lathe chuck (6 jaw 12.4") to dial in the shank as close as I can to zero TIR (I can fiddle more, but got it less then .00015". The inner taper is what is out of whack. I can't find any other seller with a ER50 collet chuck that is not CAT50 type holder.
The collet set I got say's 0.0003 TIR. From my early measurements that looks about right.
So the question, can I grind the collet taper true, and will this still let the collets live close enough to the geometry they were designed to fit in.
I need this big of an ER collet as the grinding hubs are for 1-1/4" wheels, and that is what I'm going to use as the surface datum and machine the 3"/foot taper concentric to that.
In the video, my first test was the original wheel hub that came with the surface grinder. The runout on that is horrible. Yes it's to the outer circumference of the hub, but golly, it should run with the error of the ER50 chuck, around 3 thousands TIR. Video may tell all my issues. The video clips are not in original filming order. I tested the original grinding hub first, then put in the test bar. Then filmed the outer shank and main body. Then the inside taper, to sort out where the error was.

 

[metric_taper]

I just rechecked the original grinding hub in this ER50 collet chuck. I must have had it mounted wrong to get the 10 thou runout from the previous video.
I checked the taper of the hub, and got similar results.
So I need to regrind the ER50 collet taper.
Anyone have any useful knowledge in doing this sort of repair?

 

[Flyinfool]

If you are going to try to grind it in better, I would put it in a 4 jaw and spend a lot of time getting the mounting shaft as close to perfect run out as possible. You have a half thou run out in the 6 jaw chuck you are starting from. This means you will never get it to run any better than your starting setup.

Can you contact where you bought the collet chuck from and see about getting one that meets the advertised specs? Once you start grinding all warranties or options for return are gone.

 

[metric_taper]

If you are going to try to grind it in better, I would put it in a 4 jaw and spend a lot of time getting the mounting shaft as close to perfect run out as possible. You have a half thou run out in the 6 jaw chuck you are starting from. This means you will never get it to run any better than your starting setup.

Can you contact where you bought the collet chuck from and see about getting one that meets the advertised specs? Once you start grinding all warranties or options for return are gone.

I understand getting it as perfect as possible. I can always change out the Bison chuck with the Pratt Burnerd 4 jaw I have. The bison is effectively a 4 jaw with the zero set feature. It is adjusted exactly the same way.
I did contact the seller (icarbidemachining), this was their reply:

I sorry to hear about this run out

Please try to turn the shank 40mm or knock it easily by rubber hammer or brass ,and let the run out meet 2 ten thousand

Then tighten the yaw chuck and try it again meet to low run out

thanks
Alex​

I don't think this seller will be much help. I made it clear I had a zero set chuck. But after this reply, I don't think the seller has any machining skill. On a positive note, this ebay seller, is only selling metal machine tooling and consumables, mostly ER collets. All I can do is file a not as described. However they were the only seller on eBay, or anywhere else that I can find an affordable ER50 collet chuck. No one else had the Weldon shank that I found. Mostly CAT40/50 CNC machine tapers were common, and I bet the runout on anything in the dollar amount I'm willing to spend will have more then the 2 tenths runout they advertise.

I'm going to try and dial in the taper. Then see how much runout there is with a collet installed. I'll check at the nose, and out a few inches, as that conical radial runout is a real issue that I can't adjust out. I hope this is not the problem, as any grinding of the gridner hub tapers will copy that runout error.

I have watched sever youtube videos, of what I consider crazy use of an air grinder, never intended for precision tool post grinding. And the final result's show it in bad surface finish. One guy was using a cutoff wheel, as that was the only 3mm shank tool he had outside of cheap glued on wrong grit stones for these die grinders.
I have a decent tool post grinder.

 

[Flyinfool]

I always love the option of get a bigger hammer as a vendor solution. Just beat on it till the run out is what you want.

 

[metric_taper]

On a positive note, the seller on ebay refunded my money. They are working to see if they have a ER50 tool holder that supports the 2 tenths TIR advertised specification. We shall see.
So now I'm free to try to grind it true.
I'm looking for how collets are made, and if they can be reground to improve runout. I assume the 8 degree face is spun on an arbor with a grinding wheel to make that conical section. I can't find a single youtube video on that subject. A few on grinding the taper of an ER chuck. Only one done with a precision grinder.
Metrology looks like the runout is done on a surface plate with V blocks. In my lathe setup, I am seeing a non radial runout that changes with distance from the nose of the tool. Some sort of conical runout as the bore hole of the collet is at an angle with the chuck centerline.
In the attached video, I made the taper of the ER50 chuck have a minimum runout, then installed a 1-1/4" collet with a test bar.