spindle deflection on 30 taper machine

Hello guys,

I am here again, with probably another issue, I hope it won't be another major one...

So, I am now talking about my Kitamura BBT30 machine, I am currently running a job, which I normally run on my Robodrill, and it runs fine although there are minor chattering problems on radiuses on the outer profile nothing too drastic, I am now running the same job on the Kitamura, and it seems that it just can't do it, I had to half the depth of cut to obtain something reasonable...

Now, although there could be something wrong with my setup, I think there could be also something wrong with the spindle maybe?

I had the spindle rebuilt and balanced 6 months ago, I tried today to put a dti , there is maybe 0.0001" or less on the spindle taper, the finish of the parts is very good, on both faces and side milling.

I have also tried to put the dti on the actual tool, about 2.5" gauge line, and if I push hard I can get 0.001" deflection, on another test on another tool holder , if I push it, it seems like there is about 0.0003" ""permanent"" move.

On top of this, at speeds above 6000 rpm, there is a light but annoying whistling noise coming from the spindle.

Thanks in advance

barbter said:

Drawbar retention pressure?
IMHO, the Kitty "should" be more rigid than a Robo.
So I'm thinking your holder is pulling out of contact from the spindle?

Or....it could be control and servos.
What model/year/control are both machines?
If the Robo is a 31 control, it will process/feed faster (and more accurate) than if the Kitty has (for instance) an old 21 control.

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Hello!

yes , the kitamura is way more rigid than the robodrill , I am thinking maybe there is something wrong with the drawbar.... I am not sure it's control and servos related , the robodrill is even older than the kitamura I have , it has Fanuc 16MB , the KIT has 16iMB

Is your deflection in the spindle or do the gibs need to be tightened? .001" does sound like a lot to me, knowing how stiff these machines are. If your machine uses the same springs in the drawbar I would be surprised if they are the problem, but since you have had it worked on perhaps something has come loose? Like the barrel that is between the grippers and drawbar. The first thing I would do is try to tighten the gripper bolt to make sure it and the barrel are tight on the drawbar. It is easy to do, it won't hurt anything trying, and knowing you recently had your grippers replaced. If either of those items loosens it will reduce your drawbar pressure considerably.

How perpendicular is your spindle to the table? As in loose gibs or head clamps. What cut are you taking?

DavidScott said:

Is your deflection in the spindle or do the gibs need to be tightened? .001" does sound like a lot to me, knowing how stiff these machines are. If your machine uses the same springs in the drawbar I would be surprised if they are the problem, but since you have had it worked on perhaps something has come loose? Like the barrel that is between the grippers and drawbar. The first thing I would do is try to tighten the gripper bolt to make sure it and the barrel are tight on the drawbar. It is easy to do, it won't hurt anything trying, and knowing you recently had your grippers replaced. If either of those items loosens it will reduce your drawbar pressure considerably.

How perpendicular is your spindle to the table? As in loose gibs or head clamps. What cut are you taking?

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Hello there,

I recorded 2 little videos just to give an idea.
The DTI I am using, 1 division is 0.002mm.

I just checked the grippers bolt and it is definitely tight.

I am not sure how to check how perpendicular the table is to the spindle, I checked with a clock once, and everything looked flat within 0.01mm , that might still not be the check you mean?

The "permanent" movement is radial without pushing the tool holder mega hard, I don't know.....

I tried to push the actual milling head, but it does not move at all

The cut is about 5mm deep, using a 20mm e/mill, in the deepest point I am taking 16mm radially, F600 mm/min, SS 5500rpm, the material is aluminium medium strenght.

poxino said:

Hello there,

I recorded 2 little videos just to give an idea.
The DTI I am using, 1 division is 0.002mm.

I just checked the grippers bolt and it is definitely tight.

I am not sure how to check how perpendicular the table is to the spindle, I checked with a clock once, and everything looked flat within 0.01mm , that might still not be the check you mean?

The "permanent" movement is radial without pushing the tool holder mega hard, I don't know.....

I tried to push the actual milling head, but it does not move at all

The cut is about 5mm deep, using a 20mm e/mill, in the deepest point I am taking 16mm radially, F600 mm/min, SS 5500rpm, the material is aluminium medium strenght.

Click to expand...

I'd think a 20mm endmill is about the limit I'd try in a 30 taper, even a BB. Could you post a picture of the cutter and holder assembly? Have you tried a 16mm tool?

Milland said:

I'd think a 20mm endmill is about the limit I'd try in a 30 taper, even a BB. Could you post a picture of the cutter and holder assembly? Have you tried a 16mm tool?

Click to expand...

Hello there!

I recorded 2 videos to show the problem, but I am not able to upload them, how do I do that?

yes 20mm is a pretty big cutter for a 30 taper, but I don't think I am machining it too aggressively , it should be ok...

So I know you've had a lot of threads about this machine, so you've been into the machine a fair bit.

But I don't know if you've looked at the gibbs and how tight it is?

It could be the spindle, or drawbar. Or it could be the machine being loose.


So my experience with Kitamura 3x is extensive. If your little machine is built the same, it should have a gib on the side of the x and y rails, and I believe 2 gibbs underneath (to prevent lift), one on each side. I could be wrong.

IIRC I think there's a spacer under the gib screw that you would nneed to grind down that would allow you to tighten the gib further. If you don't grind down the spacer, you'll just be tightening against it and no further gib tightening action would occur.


There's also a gib for the side of the ways on Z, that is the same thing.

But there is no gib keeping the spindle way "down" (flat against) the ways. Instead, the big bars on either side of the headstock that have about 8-12 big ass bolts holding it down are what keep it "flat" against the Z way. If the turcite in there is worn and the head is sagging, you'd need to grind that down. I assume there is a shim to grind. But I've never had those off to check, it was too big a job for us to consider at the time.

DavidScott would probably know, as I think I've seen him comment that this was the only way to adjust spindle droop if the machine doesn't tram well.


I'm just laying it out there that it might be the cause of your chatter. I really really find it hard to believe that a kitamura wouldn't be as stout as a robodrill lmao.

... Then again, with as flimsy as a robodrill can be, it might be loose enough to NOT chatter when it should, just because it isn't stiff enough to vibrate. Counter intuitive, I know. lol.

dandrummerman21 said:

... Then again, with as flimsy as a robodrill can be, it might be loose enough to NOT chatter when it should, just because it isn't stiff enough to vibrate. Counter intuitive, I know. lol.

Click to expand...

This can be tested. All we need to do is convince the OP to throw a 8mm extra-long endmill in exchange for the 20mm and let 'er rip...

Milland said:

This can be tested. All we need to do is convince the OP to throw a 8mm extra-long endmill in exchange for the 20mm and let 'er rip...

Click to expand...

Hello guys ,

thanks for the many and quick replies to everyone!

The part in question , has been machined in my robodrill and that was chattering in the same points and that's fine , I knew that , but I was surprised today , it did the same on my Kitamura , actually I would say worse than my robodrill.

Anyways.... I have done another check , putting the DTI on the spindle arbor , and try to push it as hard as I can , and I couldn't see any movement , but obsvioulsy there is much less arm.

I did try to push radially along X axis the milling head , as hard as I could , and in the worst scenario the machine deflects 0.0001" but the return in position.

and yes dandrummerman21 , I had so many issues with this machine , it was abused , and operated probably by a careless operator.

How do I test well if it was a bearing problem?

is it possible that too much tool knockout would affect the tool retention, or it does not matter at all?

I have been messing around with that a while ago, making that thin spacer between the grippers and grippers bolt

barbter said:

Hmmm....strategy...
I had 2x Robos 1x with BBT Fac/taper/dual contact, 1x without. Both model E which is stiffer than your older model, and with 31 control.
The way to win with these machines is to make them dance.
Big cutters beat the machine to pieces - if you're using 2x flute and side milling, the cutter is hammering the materail as it isn't in constant cut. And these machines don't like it.
So smaller cutters and 3 teeth and the "peripheral distance" (gap) between the teeth is smaller. So less hammering, which is better for the lighter machine construction.
Also, short and stubby sidelocks. Frank Mari (Mari Tools) sells beautiful stubby sidelocks that work a treat. Overhang and stickout are your enemy with these machines.
For roughing on my BBT machine, my data is:-
12mm dia 3x flute GARR Hogmill (knuckle form rougher)(Short sidelock 55mm out) S10000 F5000 (@18mm deep & 30% stepover -T/P RADIUS 3mm) This is a trochoidal mastercam toolpath.
If your machine is a standard taper, I'd reduce feed to F3500.

So, 16mm radially I'm not surprised it's objecting.
I'd reprog with a 12mm and bang the feed right up.
Use G05.1 lookahead for your contour accuracy and all will be well.

Edit - one thing to think about these small machines and "heavy cuts"...look at the pull stud neck diameter.
You're asking the machine to chomp a heavy cut with a holder being restrained by a 1/4" diameter...

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Hi, thanks for the tips, they do make sense for small and light machines!

Don't confuse a 30 taper Kitamura with other 30 tapers. It is an 8,000 lb box way tool and die mill with 925lbs of drawbar tension. EVERYTHING is beefier, including the coolant tank which weighs around 500lbs. The neck diameter of the pull stud is 8mm and it uses grippers instead of balls. I don't think I have ever made mine complain about a cut in the 8 years I have had it. When I push too hard either the endmill or the part moves, the machine just keeps purring along.

The way you adjust tool knockout is where the air cylinder attaches to the yoke, PERIOD! If that doesn't work then your spindle coupling is attached to the spindle motor in the wrong location and the pin is bottoming out in the slot. I know this all too well, it is real easy to do, the slot in the coupling is just long enough with very little extra room. Is the yoke clear of the ring on the spindle coupling when a tool is clamped? There is a cover on the right side of the head, opposite the tool changer, that is easy to remove so you can see it.

I really like corn cob mills for roughing aluminum. For my 1/2" and 3/4" roughers I just use HSS coated 4 fluters for steel. They work perfectly fine as long as they get plenty of coolant, even slotting, and are a lot cheaper than carbide. 3/4" is my standard rougher. I will second the stubby sidelocks from MariTool, but they only go up to 5/8".

Dan is right about everything but having gibs under the table, those are just there to keep the table from lifting and have around .005" of clearance. The gib barrels are soft enough that you can lathe them down. If you need to tighten the gib by .0005" then you shorten the barrel by .005", 10 to 1. To tighten the head clamps you pull them off and grind them flat, or leave the turcite proud and scrape them in from there. The way to check if your spindle is perpendicular to the table is to swing an indicator 6" or so out from your spindle. To do it right you should check Z axis squareness with a granite square first. Not that you can do much with the leveling bolts to square up the Z, the most I can change is about .0005" over 14". While you are at it you should indicate your table to see how level it is along its whole travel to check for wear in the turcite.

I doubt your problem is from your machine being loose. I would suspect spindle bearing preload is off or drawbar. If your preload is off you would probably see swirl marks in the bottom of pockets, usually where you plunge down to enter, or the floor in the corners where the mill squeals. If it is your drawbar then look for fretting on your tool holders, but you don't want to wait till you see any as it is really bad on everything. My Kitamura is the first 30 taper mill that I have run that I have never seen fretting on any tool holders, and I have run it far harder than any other 30 taper, which is all about it having a lot of drawbar tension.

Have you blued up a nice holder and checked the taper contact?