Milling finish

[SignalFailure]

I made this bronze part (about 1/2" deep x 1.25" long) on my new micro mill yesterday using a 10mm end mill. Overall the finish is good but the vertical face at the right-hand end has a tiny 'step' (where that last white vertical line/flash reflection is).

When I turned the piece around and did the other side exactly the same thing happened. Fortunately I can rescue the part with some judicious filing ;D

Can anyone suggest what the cause of this 'step' is?

Thanks in advance!

 

[Noitoen]

When you do the "finish" cut, you should feed in a direction such that the mill doesn't "pull" or dig into the work. The backlash in the tables feed screw nut, if you feed in the same direction as the cutting action, will pull the part as you move.

There can also be other problems. Wait for more experienced opinions :big:

 

[scoop]

Looks like the gib strips might need to be tightened a little on the axis causing the ripple finish.If the table movement is a bit loose it can cause this.

Good luck Steve C.

 

[tmuir]

I take it you weren't climb milling?

Have a look at my thread here to see what not to do.
http://www.homemodelenginemachinist.com/index.php?topic=4767.0

 

[shred]

Cutting with the side of the mill? end mills bend away from the work as they get deeper and if the step matches where the flutes stop at the top of the part, that would cause a little more bending.

 

[SignalFailure]

Thanks for the suggestions all. I think scoop is onto it - looking carefully at the table movement it does seem to 'waddle' across a little....I'll tighten up the gib strips and see if that fixes it

Cheers

Paul

 

[scoop]

As well as the loose gibs,a poorly aligned leadscrew can make it worse.If the mill handle has a regular tight spot at the same point in each revolution as you are feeding it pulls the table to one side or the other as the leadscrew pushes on the nut.Not much you can do about that without dismantling the machine though.

best regards steve c.

 

[Jasonb]

If the vertical step is about 5mm (half cutter dia) from the end which it looks like given the overall length of 1 1/4 (32mm) this would be caused by the endmill being pulled into the work by the load of the bottom cut pulling it into the side face. As the mill broke through the end of the piece it was not being deflected so sprang away from the face.

Look for any play or take lighter cuts.

Jason

 

[DavesWimshurst]

Paul
My Clausing 8520 mill needs to have the y-axis locked tight when end milling the top surface of a block or a small step is formed. It seems that the shift in the x-axis position of the table causes it to rock a little changing the depth of cut. Doesn't seem to happen with my larger but well worn Leblond which has a much wider knee. Hope this helps.
Dave

 

[sportandmiah]

With my HF micro mill, I find that I lock down any axis I don't need when milling. I also locked the drill press handle as well as the...I think it's called....the spindle? Not sure, but it's hex screw on the right side, making the only way to move the column up and down is through the top wheel. I also have been tinkering with the gibs, trying to find a decent setting. Also check the, unknown correct name, part under each table... there is a rectangle part that is split. This is where the feed screw goes into. It can be adjusted to eliminate a little friction. Wow, my english sucks.

 

[Julian]

May be worth clamping a peice of waste metal on the end so the mill cuts across the end and onto the waste as if it is one piece. When the waste is pulled away the edge should be perfect as the cutter will not have done any damage. Works for me.

Julian