Thread: Grinding a Hardened Tailstock Bore

Hi Bryan,

I'm learning this game too, but from what little I know 60 grit should be fine.. I would have thought 27/32 would have been too big, but then I don't know what size your tailstock is...

I'm guessing that you'll setup the tool post grinder on the cross slide with the compound swung around backwards at the the taper angle and lock the tail stock position and use the compound to do the grinding?

Regards
Ray

Ray, it's MT4, so the small end is 25.9mm.

I intend to set the quill up conventionally - with a chuck and a steady. I have a plan so cunning you could paint a smile on it and call it a politician.

Hi Bryan
I have heard of this being done with a die grinder burr in a die grinder mounted in the toolpost.

Phil

I am not a expert but I would have though it to be a job for a reamer

Bryan,

Dumore have downloadable instructions for their tool post grinders -

Dumore Corporation -

There is information regarding internal grinding. It may be worth a look. What do you intend using as a grinder?

BT

Bob, Phil, I have been offered a loan of a Waldown, and have a copy of the manual, but will read the Dumore one also, thanks.

China, in this case I think a reamer would be short-lived. A file skates off it.

How bad is the bore?

wet and dry sandpaper on an arbor might be an option..

How are you going to set the correct MT4 taper half angle of 1.4876 degrees ( 1.49) ?

Originally Posted by .RC.

How bad is the bore?

wet and dry sandpaper on an arbor might be an option..

Agreed. I have no idea of how bad your tailstock bore is, but if it's hardened then probably not too bad and I'm guessing the ridges you're talking about are from where some tapers have turned within the bore. They can be sanded back down and the grooves then left won't affect the seating.

I don't think grinding an accurate taper is especially easy, and unless your bore is currently unusable, the potential for screw up would far out weigh the potential benefits IMHO. There's a high probability that your angle wouldn't be absolutely perfect, and then nothing will seat right from then on.

In addition to what Richard suggested (which would probably be all it would need in reality), just thinking out loud here, but if it were me I'd probably be looking at buying a soft MT4 taper with plain turned end, chucking it in a 4 jaw and dialling it in until it is dead nuts on, then using that to lap the tailstock bore with it in situ. At least then you know what you're doing is indeed at an MT4 taper and not something approximating it (obviously check the taper when you get it), and the work you're doing to is concentric with the headstock bore. It would assume that your tailstock is indeed at centre, and if not would give you an excuse to make it so.

I must emphasise that I haven't done the above, so may well be talking out my clacker, but if it doesn't work for some reason (and I can't see why it wouldn't) then the chances are you won't have done any real damage. As a bonus you get to keep your (now charged) MT4 lap as a momento

Pete

What about using coarse automotive valve grinding paste .

Use a good new MT4 sleeve and grind/lap it into the bore . Depends on which is the harder steel though, the bore or the MT4 sleeve . It might just wear away the sleeve and do nothing to the bore .

If you do try the paste, try and find the good stuff , I've noticed the modern paste (power plus is one) is somewhat weaker than the older brand pastes . You could research it . MIKE

On further thoughts, if confident enough to grind an internal MT4 taper, I wouldn't even bother buying the morse taper. Just machine up a lap to MT4, much easier to cut an external taper, and if you screw it up you just keep cutting

Charge it with abrasive medium of choice, and lap away! When finished, admire your now shiny bore and sell your custom made MT4 lap on ebay!

Pete

Using valve grinding paste between two mating tubular surfaces can be a bathed in sweat experience. They tend to lock together. I replaced the bronze guide bushes for the round bar arm of my Lotze power hacksaw. They jammed tight on the bar when I used valve grinding paste in an attempt to remove a thou or so from the bush bore. Might be ok for removing ridges.

BT

Originally Posted by .RC.

How bad is the bore?

wet and dry sandpaper on an arbor might be an option..

Attached is a pic of the worst part of the ridge. I haven't found a way to measure it. Feels huge but might be .3mm high. Or less.
Sandpaper? Lapping? How could these be more precise than a TPG?

Originally Posted by Retromilling

How are you going to set the correct MT4 taper half angle of 1.4876 degrees ( 1.49) ?

By clocking the existing taper with a DTI in the tool post. A short section of it anyway.

Originally Posted by Bryan

Attached is a pic of the worst part of the ridge. I haven't found a way to measure it. Feels huge but might be .3mm high.
Sandpaper? Lapping? How could these be more precise than a TPG?

How much internal TP grinding have you done?

That bore doesn't look too bad to me.

Sandpaper and lapping are, in this instance, repair operations intended to repair an existing bore ie presumably what you want to do. I have successfully used wet and dry on an unhardened tailstock bore to remove ridges and it worked perfectly.

In contrast, grinding is really a machining operation which I definitely don't think is appropriate in this case.

If ever I had a tailstock so bad that it needed to be ground, personally I would look at making a whole new quill, not hardening it, and reaming it. But that's just me, and besides I don't think your bore looks that bad at all. Maybe it's just the photo being kind.

Pete

Edit: just for clarity, the reason I'd approach a trashed tailstock this way (ie re-machining from scratch) is because of many other advantages in machining a tailstock bore with it in situ on the lathe on which it will be used. Not much point in going further into this however.