Difficulty Fly Cutting on a Benchtop Milling Machine

[erikmannie]

In the case of a z-axis cut on a benchtop mill, it sounds like the proper method is to:
(1) take up lash while raising the head, and
(2) lock the z-axis.

Question to ponder (only talking about milling machines here):
(1) If a shop uses only RH cutters, are they advised to take up backlash solely by clockwise rotation of a handwheel? In other words, “to feed against the force of the cutter”.

 

[erikmannie]

When I went out to take pictures of the stand bolted to the floor, I can see that *there is play*. This is definitely an issue.

The stand does not rock back-and-forth or side-to-side, but it rocks a fair amount across one diagonal.

How would you guys fix this? The lazy way to fix it would be to just hammer in a shim.

I think that tar paper would take up the slack, but I still don’t love the idea of the stand only having 2 anchor bolts. 3 points are required to determine a plane!

 

[jwmelvin]

The gibs have the factory adjustment.

I’d certainly check to see if they can be tightened up to remove some of the excessive slip you’re seeing, without introducing too much drag.

 

[mikey]

Just a few comments, Erik.

• It might be a crappy fly cutter or it might be too big for your machine. Sherline makes a 1" diameter inserted carbide fly cutter that is superb; it might be more suitable for your mill. I can take a DOC 10 times the cut you tried to take in steel on my Sherline with this flycutter.
• I agree with jwmelvin. Lower the cutter below your intended setting and then raise it up to the setting you need. This removes the backlash in the system.
• I really don't think the bolts on the base are an issue. My Sherline mill attaches to a board that is not attached to anything; the mill just sits on a table and it works fine. My RF-31 sits on a sheet metal base that is on casters and it has zero issues taking some pretty good cuts. Bolting a mill to the ground is unnecessary in my experience.
• You might want to explore why the two Z-axis bolts are coming loose. Something is not fitted well if the head is vibrating loose.

 

[markba633csi]

The carbide tool is probably taking a lot of force to push- can you try a very sharp HSS tool instead?
I agree the diameter might be too much for a small mill like that

 

[erikmannie]

The carbide tool is probably taking a lot of force to push- can you try a very sharp HSS tool instead?
I agree the diameter might be too much for a small mill like that

I have a tool bit in that size, so I can try that.