[pyroboby]

Hi guys,

Got a question for you. I was trying to make a .071 inch slot with a .062 end mill. Had a guy at work help me with speeds and feeds. First attempt at .02 DOC resulted in the end mill breaking at the very end of the slot. Next attempt another end mill broke near the beginning.

Went to work today and talked to a few people and they told me to check my runout on the spindle. I put a 1/4" end mill in a DA180 collet holder and checked it out. Its a little over .0015 which I was told is no good for tiny end mills. What is the factory spec run out for the spindles on these? How difficult is it to repair this. Is it just a few bearings? Or does the whole spindle need to be pulled and sent in to someone? Thanks all.

Rob

[machintek]

This is why I send a spindle out for a rebuild. It is fitted with new bearing, pre-loaded correctly put in a fixture and the spindle taper ground as it is running in the bearings so there is minimal runout. The spindle is a cartridge (assembly).

George

[keebler303]

You sure it isn't the toolholder, collet, etc.?

Measure the runout on the actual spindle taper.

Try a different toolholder. Rotate the toolholder 180 degrees and see if the runout follows the toolholder.

Measure the runout on the toolholder taper.

Matt

[pyroboby]

I tried several tool holders, roughly the small reading. How difficult is it to remove the spindle? I don't have a manual for a diagram on what it even looks like in there.

[keebler303]

Check out the attached picture. Hopefully you can just unscrew the nut on the bottom of the quill and pull the whole deal out. I don't know if you need to take the quill out or not. If so, take the front cover above the quill off and you will get an idea of what you need to do. There are six cap screws that hold the quill to the ballscrew. You would have to remove these, then the quill should drop out the bottom, assuming there is enough clearance between the head and the table.

If you can't get it out going down, you can go up, but it requires taking apart almost everything on top of the head. I just had mine apart to replace the bearings on my Z ballnut. I would surely try to drop it out the bottom first. Might be able to loosen the bolts holding the head to the casting and rotate the head a bit to get the quill out. The spindle has a long splined shaft on it so it will need some room to get it out. I've never taken mine out so I can't say for sure how it is best done.

Good luck
Matt

[pyroboby]

Would vibration caused by something in the varispeed contribute to breaking those little endmills? Read on a few places that a plastic part wears out and causes vibration. My spindle is by no means quiet when it runs.

[keebler303]

There are plastic bushings inside the varidrive pulleys. They could make noise. A while back I replaced all the bearings in my head and replaced the bushings as well hoping it would quiet down the spindle. It did not. I think the worst of the noise is from play in the splines between the drive bushing in the head and the spindle. If you apply the brake and your spindle rotates a little bit back and forth, your splines are worn. The only way to fix it is to replace that splined part in the head. I heard it was expensive so I have learned to live with the noise.

I wouldn't think that amount of vibration would break your endmill. If you have runout, I would track that down before looking elsewhere. Did you check runout in the spindle taper?

Matt

[pyroboby]

Yes sir, I checked it last night, its just over. 001. Yeah, my spindle moves a bit when the brake is applied.

[keebler303]

I think part 33 here is what you need to replace to get rid of the slop in the splines: 1.5 - 2 HP

The spindle spline is probably worn a bit too so you'd only fix half the problem replacing that. I doubt it's the cause of breaking endmills.

What speed and feed are you using? I'd normally use 3000 RPM 20-30 IPM with a .02 or .03 stepdown cutting full width.

These machines aren't the best for small cutters since they are .001" per step you don't get a smooth feed but a bunch of little pulses which small endmills don't like.

I'd recommend just backing off on your speed and feed until the endmills live and then be happy you have a mill.

Matt

[pyroboby]

I had a .010 doc at 2500 rpm and 10 ipm. I am happy I haves mill, just trying to see what I can do with it. I am planning on upgrading to newer stepper motors to get microstepping but I need to either save up or get some work for them.

[keebler303]

I'll have to check the runout on my machine. I have broken plenty of endmills, but they have mostly been F-ups on my part, not just spontaneous breakage.

No offense but you did have the gearbox in high with the spindle going the correct direction right? I can't believe a .01" cut at 10 ipm would break your endmill, even with a little runout. The speeds I mentioned were for aluminum, what are you cutting? Are you plunging straight to depth or ramping in? Any coolant/lube?

Matt

[John Bennett]

Reading post, you are using a 1/16 endmill (you have not stated how many flutes) . I would presume that this is a HSS endmill. What material are you cutting and to what depth per pass? If you are using say a two flute endmill in 6061 aluminum, then you are about double what, I calculate, your feed should be. Give us all information to recheck your feed and speeds.

[keebler303]

If 2 flutes, that's .002" per tooth at .01" depth. Seems like that should be alright. I guess it depends a lot on what the tool is, cutting length, etc.

Matt

[pyroboby]

The end mills were carbide 3 and 4 flute. The material is 303 stainless, I have a feeds and speed calculator from a programmer at work. It has 304 in it and he told me to cut anything in half that it spits out for my mill.

The program suggested 5000 rpms at 22.5 ipm for a 3 flute carbide end mill. As stated in previous posts, .010" DOC. I'm not going to worry about getting it to work at the moment as I have a key seat cutter that can make the slot I need. I'm leaning towards the problem being a combination of run out, vibration in the spindle/head, and those old not very smooth running stepper motors.

Matt, spindle was running in the correct direction, I'd feel quite the fool if that was the case and I haven't taken it out of high gear for cutting yet. Its a .070" slot that is .150" deep. I was going to take it in .02 or .01 DOC then move over and start from the top and make it to width. One tool was a standard 1/16 carbide 3 flute and the other was a stub length, the stub length snapped immediately. The 3 flute made it almost all the way.

[John Bennett]

I agree with your feed if at 5000rpm, but you stated 2500rpm which for a 3 flute cutter would bring use into the range of 6ipm or start point of 5ipm.

[pyroboby]

Yeah, my brother in law works in the opposite end of the factory, he said 4 or 5 ipm. Ill be trying it later after I have a few more end mills. As I said I'm going to use a keyseat cutter for now. I wish I had the budget of my day job for home use for just one day.

[keebler303]

Yeah, it gets expensive after a while. Try to get double ended end mills when you can as they have twice as many cutters and are NOT twice the price.

Matt

[pyroboby]

Finally had success, left the rpms at 2500 and backed the feed down to 3 ipm just to be safe. Slot is all done, thanks all, im still going to look into the noise and run out in the spindle as time and money allow.