Why is Spindle Taper Getting Banged up & How to Clean Up

I have an Atrump BT30 CNC mill. I bought it new and have been running it for about 18 months now. It does not get a lot of use as it only supports a drag racing operation and I bought it because it fits my needs well.

The more I learn about the machine the less impressed I am. Factory support is poor but my dealer is trying hard - I like him. But now it is what it is.

I had to remove the spindle to correct some issues.

I was very surprised to find what I would call significant nicks in my taper. My questions are what is causing this and how best to clean up? I don't want to make it worse. At this point I am not seeing any ill effects on tool holder tapers.

- Am I inserting the tool incorrectly? I made some corrections and it seems to be engaging better than it used to.

- Do I need to round the ends of the tool holders to make sure they are not sharp?

- Is my spindle too soft? Does not seem to be very hard. How hard should they be?

- Other?

I was thinking of running it at a fairly low speed once back together and hitting it with some emory cloth to knock the high spots off. Good idea? Bad idea?

In addition, I stripped the thread on the draw bar. It has an air operated draw bar. Poor draw bar quality or could something else be going on? I have the air pressure set at 60 psi so I do not think I am over tightening it. Thoughts?

That crap in your taper looks like your drawbar had been coming apart for quite a while,
and you were depositing flakes of drawbar into your taper everytime you tightened or
loosened it. That crap could be coming from your tool holders also.

I would get a new drawbar, But I would make sure the threads were nice and clean and
smooth, maybe even put some solid film lubricant on there. Then I would go to
my tool holders, and check all those also, maybe re tap them, or even lap them. And
depending on how everything looks, maybe some film lube in there also.

As for the taper, most of that shit will probably come off. I wouldn't go at it with emory
cloth spinning. I'd start with some scotch brite, get a flash light and lay on your back.
Maybe a small pick would help peel that crap off also. A wire brush maybe.

I wouldn't do it spinning, you don't need to mess with the areas that aren't damaged, you
need to work every little spot individually, especially with an aggressive tool, or abrasive.
Scotch Brite really shouldn't hurt anything.

Bobw said:

That crap in your taper looks like your drawbar had been coming apart for quite a while, and you were depositing flakes of drawbar into your taper everytime you tightened or
loosened it. That crap could be coming from your tool holders also.

Click to expand...

Thanks! I did not think of this and it makes a lot of sense.

Any other opinions?

It looks like debris was getting pinched between the taper and the tool holder. It's hard to see in the pictures but are they nicks/voids in the taper, or are they protruding from the surface like you'd imagine if chips/metal shavings were compressed into the metal? I will assume from observing the photos that they are mostly protruding. I would be careful sanding them down; that will smooth it out but also remove the circularity making it so the tool holder does not seat properly. If the spindle material is much harder than the inclusions though it might be within an acceptable tolerance (ie hardened steel taper with soft aluminum inclusions).

Can you regrind the taper? That's probably the best solution other than a replacement. I think Bobw's idea is valid but you probably won't be able to remove 100% of it and if you can't remove 100% of it, that'd be almost as bad as removing none of it. Like you pointed out, you need to not only repair the damaged taper but also identify the cause of the damage as well so that it doesn't happen again.

60-90 psi is within acceptable range for a typical draw bar. Judging by the damage pattern that shows a concentration mostly on the back/top end of the taper I would take a close look at the draw bar or anything that sits in that space. If it were something such as chips stuck to the tool holder itself for example, you would not see such a localized zone of damage.


Joe

markz528 said:

Thanks! I did not think of this and it makes a lot of sense.

Any other opinions?

Click to expand...

Lay-in a collection of round and curved synthetic "India" stones rather than Scotchbite is all.

They don't cost all that much. You can afford to abrasively "shape' and re-shape them. If yah chance to drop one now and then? Even the bustid hunks can be handy for full half a century. DAMHIKT!

A(ny) hard "stone" will let you take off a RAISED burr. And not much ELSE.

A(ny) FLEXIBLE abrasive is not so loyally monogamous. It f**ks with EVERYTHING it touches.

Might LOOK nice, that polish. But it is slowly carrying you off-spec, more so each go. Far worse? It isn't even correcting the core problem. BUMPS that stick UP, not divots as sink DOWN.

Old-timers say "stone off the burrs". We actually do mean "stone" - just like we said we meant.

2CW

On fixing the spindle I've used Catt Spindle Grinding a couple times. I know they travel all over country doing jobs. Catt Spindle Grinding | Spindle Grinding Service & Repair There may be someone closer to you that does the same thing.

I have gone at spindle tapers with round hones..might take two hours but you can restore to near new,
Finding a big nick one can use a fine round or half round file.

Thanks for all the feedback. They gave me a great price so I bought a new spindle. Will be changing some things so hope it won't happen again with the new spindle. I will also clean up the damaged one and keep it as a spare.

Is it this one? S-8

If you don't mind the question, how much was the replacement spindle?

Milland said:

Is it this one? S-8

If you don't mind the question, how much was the replacement spindle?

Click to expand...

Its a A1-3T bed mill. $700 fully dressed with bearings. Looks to be a slightly beefier knockoff of a Bridgeport spindle. I really wanted the CAT40 spindle but could not fit it in the shop.

markz528 said:

Its a A1-3T bed mill. $700 fully dressed with bearings. Looks to be a slightly beefier knockoff of a Bridgeport spindle. I really wanted the CAT40 spindle but could not fit it in the shop.

Click to expand...

Thanks. For $700, it sounds like the right move is to replace and keep the original as a spare. Just figure out why the damage occurred and fix that before putting the new one it.

Bobw said:

Then I would go to my tool holders, and check all those also, maybe re tap them, or even lap them.

Click to expand...

Good call. I bought a go/no-go gage for the threads, and suffice it to say that at least some of the toolholders are going in the garbage. I try to stick with better quality toolholders, but some cheap stuff filtered in.

One cheap one the no-go goes right in. I only checked 5 holders, and so far only 2 were acceptable in my opinion. 2 were tight and one was loose. I will try to loosen up the tight ones - the tight ones were Parlec which I thought should be decent.