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I would add more support or shorten the grinder spindle length for less flex
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Hi all.
I bought a cheap benchtop milling machine and then found out that the spindle runout is more than 0.1 mm at the internal taper hole of the spindle, bad luck of me! Checking the bearing looks good, re-adjusting the preload nut didn’t help, now I think the taper hole itself is out of center.
Thinking to re-grind the taper hole, here’s the plan attached.
I’m not a good machinist, need some advice from the wiz here.. Will it work? Any input appreciated.
I would add more support or shorten the grinder spindle length for less flex
Nice job modeling this!
It sure will work....but with allot of skill!
It looks like a morse taper??...only taking out the very least amount will work, otherwise your tooling will sit too deep!
One other alternative...take the spindle apart and have a grinding shop doing it... probably save you money at the end.
Konrad
That seems like a crazy amount of run out - .004 thou! Can you take the mill back (is it new?). How are you measuring the run out - indicator? Can you get the indicator on a part of the spindle other than the taper hole and is the problem definitely the taper bore?
That’s an interesting set up and idea (x/z to make the taper). I don't think that I’d have the nerve try it, but admire the ingenuity). Wayne is right, it needs more support. Make sure the axis of both spindles lie in the z/x plane. Have you an internal grinding spindle? If not, acquiring one is not trivial.
Just be really sure that's the problem before you start removing material, and sending it out is not a bad idea.
Last edited by Mcgyver; 02-26-2006 at 08:06 PM.
A couple of things for you to consider before trying to grind the taper. Machine alignments. If your spindle is not parallel and perpendicular to the axis you are grinding with you will absolutely have problems. An out of parallel condition will cause the taper to grind in what we call a bow tie condition. Tight in the middle and loose at both ends. That is as bad as it can get. I don't even know a way to program around that one. You can also cause the angle to be wrong which you probably could program around, but it would be some trial and error to get it right. Morse tapers are really tricky to regrind on the machine. A small amount of stock removal will cause the tool to sit quite a bit deeper in the taper. If you have .004 TIR you could move the tool as much as .040. There is not a lot of room at the bottom. We grind spindle tapers every day, and after 25 years, we decided that we would no longer do morse tapers. Too big of a pain in the a--.
Thanks, I’ll put both on my notes.I would add more support or shorten the grinder spindle length for less flex
Yes, Morse taper no. 4, from the web: large dia. 1.231”, small dia. 1.02”, depth 4.0625”, included angle 2.975 degree. The tool holder that comes with the machine still has a spare about 1 cm in length and there’s a big bore above the taper, so I think there’s enough space to play with.It looks like a morse taper??...only taking out the very least amount will work, otherwise your tooling will sit too deep!
Uhh.. The quality of this machine already makes me sick, and I can’t send it back too!That seems like a crazy amount of run out - .004 thou! Can you take the mill back (is it new?). How are you measuring the run out - indicator? Can you get the indicator on a part of the spindle other than the taper hole and is the problem definitely the taper bore?
I measure with DTI, even without any measuring tool I’m sure it is very bad, I can see the wobble with my eyes. One thing I just learn: Never buy the cheapest one!
Nice advice from the expert! So if I will do this plan than I have to start to work one step back, aligning the table if possible. How if it’s not possible? Can I just align the grinder support plate?If your spindle is not parallel and perpendicular to the axis you are grinding with you will absolutely have problems. An out of parallel condition will cause the taper to grind in what we call a bow tie condition.
Other things come to my mind:
How to align the grinding stone on the right starting point?Thanks to all advice, need a lot more…
The diameter of the grinding stone will be getting smaller along its way, right? How to compensate this thing? Any guidance?
CI
With regard to grinding spindle tapers:
Grinding it oneself makes as much sense as doing one's own heart surgery....
Several pieces of advice:
1. Reread post #5
2. Pull the spindle,
3. find a local spindle repair shop,
4. take it there
5. let them grind it and provide Q/C certs thereafter.
6. If you think about doing it otherwise, reread post #5.
Yes this is a DIY hobby but you can't do EVERYTHING yourself.
The actual error is .002, or one half of the total runout observed with the dial indicator. I would strip the spindle completely down, remove the bearings, and set it up in V-blocks to try to see whether it might be bent, or whether it is actually poorly made. Removing the bearings may also reveal an assembly fault, such as a scored journal, interference between the fillets on the bearing race and the shoulders, etc. Also, the fit of the bearings inside the housing should be checked. They need to be a very close slide fit, or wobbling will ensue.
I know that the hobbyist most likely does not want to spend $500 to fix up a cheap mill. But to fix it up cheap requires a lot of careful work, even in a home shop. You first need to determine the actual fault.
If you were to make up a test mandrel by turning a male morse taper in your lathe (and never remove it after turning it until the tests are complete), then you might have a basic starting point to slide your spindle onto this test taper, and then determine whether the runout is real, or the shaft is bent, etc.
The best would be to make your test taper as a double ended taper, one end fitting the spindle taper accurately, before you turn the 4 Morse to test with. A very accurate center hole then needs to be drilled into the outboard end of the test mandrel before turning the final test taper, because it is entirely possible to machine a crooked shaft that has been chucked with a mis-aligned center. If everything is kept very clean, and the spindle taper was in excellent shape to begin with, you could hope for a repeatable setup, as it may be necessary to remove the thing in the course of doing the repair.
You need to constantly check everything in your setup for runout, there is no room for assumptions.
So if the bearing journal turns out to be actually eccentric, then you could do a 'lame repair' by knurling up the journal, then turning it back to size. Or, undercut it and built it up with epoxy and then machine it to size. I know, we are all cringing
It will provide several days of entertainment for you, and a friend with a lathe.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
There is so much that can go wrong here. Even us so called "experts" don't work on these in the machine anymore. And the tapers we do work on, we would never do by programming the machine. Again way too many variables that can make it worse rather than better. Seeing as this is a public forum, I hesitate to explain exactly how we fix them. I don't own the company, just work for them. And it is how I put food on my table. But let's just say in the hands of an inexperienced person it's just asking for trouble. You can try it if you wish, but a very high probability that you will end up pulling it anyway. And it might be cheaper to just bite the bullet and let someone else fix this one.
have to support NC and Hu.....ya ain't gonna make it better with your approach......well you might make it different....is that what you're looking for....
To give you a good idea, if your spindle and bearing is half descant, then all you need to do is stick in some sort of tooling, lets say a milling arbor, instead the cutter, a chunk of round steel, then clamp a lathe tool bit in the vise, cut od, then check for run out on the cut piece of steel.....good run out = sound spindle, good bearing, bad run out = spindle possible NFG
Konrad
Cutting a piece of round steel with a lathe tool won't tell you much. If it is a bad bearing, you might see some runout on the piece. You will see more runout on the side of the piece opposite of the side you cut. If the bearings are good and it's just plain old spindle runout, you willl remove the runout in the workpiece. The clamped part will still runout but not the end you cut.
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