Need Help!- Pocket milling tapering?

[Mascot1]

Hello all, Noobie here! I have a Haas VF6 and I'm having problems with it. I'm cutting a bearing hole with a 6 tooth face mill. The hole is 0.732 deep with a 3.156 O.D. I've been using the same program and tool for 2 years so nothing has changed. L22 Z-0.0333. I would use a boring bar but I don't have one long enough. The problem started about a week ago. The top of the hole is consistently .004 smaller at the bottom of the hole. It's tapering and I don't know why. If anyone has any clue as to what is causing this, any suggestions or help would be greatly appreciated.

Thanks,
K.C.

[bborb]

Use the same tool and only go .25 deep. Then use the same tool and make a new hole and go .5 deep. Then use the same tool and make a new hole and go .732 deep. Check all three hole diameters (as close to the top of the hole as possible) and let us know what you find.

[Mascot1]

Hello again and sorry this took so long. Here's what I found. Top I.D's are all the same. As they should be. It would seem that the hole has a gradual 4 thou taper by the time it reaches the bottom. Any ideas???

[bborb]

Quote:"The top of the hole is consistently .004 smaller at the bottom of the hole."

How can the top of the hole be at the bottom of the hole?

Some people incorporate a "spring" pass. This is where the last operation is performed again to "skim" the surface at the same dimensions. This is to cut any material that was left from the previous cut's tool deflection from tool pressure. See if that helps, and let us know.

[Mascot1]

[QUOTE=bborb;503348]Quote:"The top of the hole is consistently .004 smaller at the bottom of the hole."[QUOTE]

Very sorry about that. I read that after and realized my mistake. I tried to edit but there was no edit button showing up on that posting. This problem made it a very long day. lol!

What I ment was the bottom of the hole is consistantly .004" smaller than the top of the hole. The top of the hole is the correct size. It starts tapering roughly around .170" to .200" down into the hole.

I tried doing a skim after under sizing the finish cut by .002", and it some how made the top come out oversize by .002". I did this by changing the tool size in the offsets screen so as not to alter the program.

[Mascot1]

O.K. I altered my "I" dimention .002" smaller instead of altering the tool size in the offset screen. I will then run a "spring" pass adding the .002" back on to see if that does it.

Fingers crossed!!

[Mascot1]

Nope! Still tapering. Now the bottom is .002" too small and the top is .002" too big. Time to call Haas??

[Donkey Hotey]

Is this an inserted mill? Is the toolholder shank worn? Held with a collet? Is the taper worn? Is it being held in the spindle tightly?

[HuFlungDung]

Relevel the machine and check the squareness of the spindle to the table. Had any crashes in the last 2 years?

Here is a thought to check right on the part: mount a suitable dial indicator in the spindle and run it up and down (not sweeping) the bored hole. Do this on the quadrant lines. If the indicator stays steady (meaning that so far as the spindle is concerned the hole is true), that would mean that the spindle is not squared to the table. However, the taper effect may not be the same in both X and Y, so you might be able to figure out which way to adjust the jack screws under the machine.

[Mascot1]

I have checked the hole with a dial indicator. .004 from top to bottom on the y axis and .0035 on the x axis. Does this mean my machine is unleval indefinatly?

[Mascot1]

Originally Posted by Donkey Hotey Is this an inserted mill? Is the toolholder shank worn? Held with a collet? Is the taper worn? Is it being held in the spindle tightly?

My machind is a Haas VF6... What's an inserted mill?? Sorry, I'm a noob! Tooth holders seem to be fine. They were alwayse a little bit rough, but I haven't crashed that tool since I started this job 2 yrs ago. Lesson learned!! The taper is clean, tool is being held properly. Spindle PSI was checked by Haas last month.

[Boots]

Check the Seats in your tooling to be sure the inserts are indeed setting sguare. If one insert is canted and not square this is all it would take to spoil your day. After doing this same job for 2 years things will start waring out. Inserted tooling , by nature, pounds off the metal and damage to the inserts' seats can cause a problem. It just may be that simple. If your head is unsquare with your table then you would have a different condition than what you state inside the bore. If this bore is for a bearing then it has to be very accurate. Most bearing bores have to be machined to a toll. of (+) or (-) .0004 so you have to figure this out quickly. Consider new or different tooling.