Need Help!- Question on turning Wood Bat

[Minna]

Hi,

I am turning a Wood bat on a cnc hobby machine. I am New to this and finding that when my program gets near the handle of the bat to turn. My machine begins to Vibrate and make Horrible cuts, causing the bat to snap.

My Question is, why is this happening?

Does it have to do with the cut depth/feedrate/tooling/spindle speed?
And if so how do I correct this?

Any help would be great..

Thank you.

[ger21]

Any pics of the machine? What tooling are you using? Climb or conventional cut? feedrate? depth per pass? spindle speed?

[Minna]

Couple of pics,


Feedrate has been from 8in/min to 33in/min
Spindle speed 700-1150
cut depth, 1/8in - 1/4in

Can't seem to get a smooth cut over that handle area,

What do you think?

[ger21]

You may need a steady rest, but try lighter cuts. You may need a different cutter geometry as well. Looks like a metal cutting tool. You want something extremely sharp for wood.

[Minna]

Thanks, where would be the best place to look for that sharp wood cut tooling?

[cam1]

Hi:
Some observations/comments: Nice Machine

1. Cover the ways with rags when you cut wood, the dust will get under the saddle, and stick to the lubricated surfaces.

2. Use an HSS square tool, grind it really sharp with lots of rake in all directons.

3. I sometimes use a groove turn toolpath to make long slender shapes. Groove turn toolpaths plunge into the diameter leaving just a little stock, and then retract. They remove most of the material, leaving the part ready for a finish pass. In your case you may want to break up the toolpath to rough machine the portions of the bat where the most material needs to be removed, and then do many light finishing passes. Wood is tricky, as it's very elastic, and it's whipping on you at the center. Try slowing the speed and reducing the depth of cut.

regards

[Geof]

The suggestions for the cutting tool are the correct approach; wood needs something similar to a knife edge slicing the material off.

Another approach with long slender parts like that is to turn it around, and have the handle end near the chuck. It is difficult to see if you are doing it between centers, but if you turn it around and grip a bit of extra length in the chuck you will get better rigidity near the thinnest section. Also have a split metal sleeve to grip it in so the jaw pressure is spread over a larger area.

Using this approach you finish all the turning except the top end of the handle, and do this last...very carefully, until you have almost parted it off from the length gripped in the chuck. You do finish up with a small tip that has to be hand sanded.

[Art Ransom]

A common problem is too much pressure beng applied by the tail stock causing the material to bend. From the pictures it appears that the maerial is whipping/flexing. I have turned several bats on my manual lathe and whip has not been a prblem. You speed seems ok, maybe even little slow. I woul start with changing max cut depth to .1" and finish cut to .05 with 100 IPM feed. Also you might try using a bowl gouge as a cutting tool.Keep us informed with your progress.

[Minna]

Thanks,

So I will try the cut depth to .1", Feedrate is ok at 33IPM I would like it faster however it seems like it's getting caught/skip on the wood sometimes. Is that due to the spindle speed being to low? What spindle speed do you suggest?

[Art Ransom]

I use a router on my indxer which doesen't help in your case. Also when turning manually I adjust speed so it feels right. Tear out is mainly a combunation of speed, depth of cut and tool sharpness. You will have to play around with these.

[Minna]

When cutting wood, where is the best place to come in to cut?
Right at centers/Above/Below.

[cam1]

Hi Minna:
DNC (dead nuts centered) I'm assuming that you are referring to the setup of the cutter with respect to the center of rotation. On some very heavy cuts some people take the deflection of the tool into account, and set it a touch high, so that it goes to center when it deflects. I've always set my tools on center by taking a light facing cut on a piece of stock. You are on center when the "tit" on the center of the stock is removed.

regards