Need assistance with a milling job

Gentlemen,

Let me start by saying I am not a machinist by trade.

I work for a metal fabrication company, where we laser cut, bend, and weld.

We have some small jobs requiring us to move .328" in from the edge, then plunge down .125" then mill a slot 1/4" wide x 1/2" long, the part we are machining is 3/16" thick.

I am running into problems with starting the cut. I am using a 1/4" 140 degree spotting drill, going down .123" to start. Then I am switching to a 1/4" 2 flute carbide endmill, I lower it into the pre drill hole, then start the cut.

After pre drilling, when I lower the endmill in and start moving. A bone shape develops at where I start the cut.

Can anyone help with preventing this from happening, the deformation doesn't seem to be happening when I lower the endmill in, but I may be wrong.

I have tried just straight plunging with the 2 Fl endmill, and 4 Fl endmill no pre drill hole, with the same results.

I will attach a blueprint, and photos of the machining process, to help better understand.


I am using a manual Bridgeport clone made by JET.

Import R8 tooling for the endmill, and a import drill chuck for the spotting drill.

Thanks in advance.

Here are some photos

What material? Cheap endmills are false economy, even if everything else is low end import buy decent end mills that are made for the material at hand.

Without seeing it you are probably getting chatter from the setup not being rigid enough. A work around is to use a 3/16 end mill, cut down the center of the slot, than move a 32nd off in each direction to get the desired 1/4".

One more idea- do a manual ramp to depth rather than plunge, crank on X and Z at the same time to get to the bottom rather than spot drill.

Edit: you posted pics while I was typing. Run back and forth with a 1/4", then finish and get the radius with a 9/32" EM.

How far are you extending the quill to your workpiece? You will want to keep that as short as possible to reduce deflection from the quill. In my opinion the spotting drill isn't necessary on that short of a depth. Also check the run-out of your tool while it's chucked in the collet. If there is excessive run-out try a different collet if you have one. A good quality end mill will be a night and day difference as well. I would use a 3 flute end mill personally with the shortest flute length available. Also if you lock the table in the axis your not feeding may help as well depending on the backlash that's in the machine. Hope this helps.

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If you are seeing a oblong in the very start of your milling operation and it only appears on one side at the start then your most likely experiencing table movement, the load of the cutter forces against the end play in the table.
Pretty common, check your jibs and remove as much end play in the X-Y movement as possible.

as per others, reduce stickout, use a high quality end mill, use cutting lube, if getting chatter reduce speed, are you locking the quill? cranking up the knee to plunge? if you put an indicator in the spindle and grab the table and try to move it (put your shoulder into it!) what kind of movement do you get? you are locking the axis not used for the cut travel, yes? try "riding the lock" to reduce play on the axis used for the cut. and yea, you really don't need a pilot for this!! (with a center cutting mill)

It looks like you are making the cut on the Y (front to back) axis with the X (left to right axis) left unlocked.

Try locking the X axis down for the cut. Then unlock it to move to the next one.

Another thing is the gibs could be loose. Check them and have them as tight as your work movements will allow. And, of course, there is backlash in the screw and handwheel. All of these problems should go away when you lock down the X axis.

What everyone else said with locking down x and using a good endmill with mist coolant or at least air.

Not sure what your tolerances are on the slot but if they are tight and you can't get rid of the x axis slop, then use a slightly undersized endmill to rough the slot and then do a finish pass to take it to dimension.

Teryk

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Thank you for all the feedback

I am locking the quill and the table, And moving the knee up to plunge.

Using a kool mist.

I am using a garr 2 flute endmill, that is seated as far up the collet I can. Has anyone else had problems or any experience with garr endmills.

I will try locking the table and see if it moves in any direction. And check the run out of the collet.