Flycutting issues...??

EmilioG

EmilioG

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H-M Supporter Gold Member
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Jul 20, 2014
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I’m having a problem on a BP mill, flycutting any metal, where it’s cutting heavier on one side , X axis, even after tramming the mill and indicating the vise. This is on subsequent passes after making the top flat.

What could be the problem? Am I incorrectly tramming the table? Could the table be warped or the vise bed? Parallels?

The table is not in great shape but I was able to tram it, so what could I be doing wrong?
BP vari speed J head. R8 fly cutter.
Cheap Chinese lathe tool.
Parlec vise (not in good condition.

Spindle run out? (Need to check).

What can I look for? Thanks
 
Can you post a picture? The part is tapered in the X axis?
 
How are you tramming the head? Is the quill lock working properly? Are you adjusting knee and if so are you locking it?
Indicate your part after you lock everything down. Then indicate after cut not touching anything.
 
Does your cut start or end heavy? Could be your cutter is slipping.
 
The cuts end as if the X axis is off a bit.
I’ve trammed the mill 3x. Everything is square.
I check after all the bolts are tight. Still... ?
I’ll check for slippage.
 
As @Cadillac suggested, your knee could be ''rotating'' I had this problem with mine until I tightened the gib. Lock the knee and see if that makes a difference.
 
How do you tighten the knee gib? What tools do I need? Thank you.
 
Before you do this, lock the knee locks and take another test cut. If that fixes the problem then tighten the gib.

A large blade screwdriver and a phillips screwdriver. The gib is on the left side. Remove the top and bottom wipers, there should be screw heads under both. Loosen the bottom screw, and tighten the top screw. Make sure the the knee doesn't bind at the top and bottom. When the gib is adjusted to your satisfaction, then tighten both screws and replace the wipers.
 
What are you trying to surface. If the part is 1/2" and less it could be bowing from the forces of the vise. Which is what I tend to do. Confident in my vise I release pressure on the finish cut when trying to do thinner pieces. If it's a chunk disregard but it still can be moving.
 
Easy, clapped out Bridgeport knee mill.
If the parts are short <10" place the vice at one end of the table, as close to the end as possible. The ways will very likely be less worn at that position, do not move the knee once locked. Do the work at one end of the Y axis for the same reason.
Try it and report back, you may be surprised by the results.
 
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