Bigger cut with tiny mill?

[dontrinko]

What do I need to do to get bigger cuts on my Unimat set up as a mill. Typically I use a 1/4" mill and the slowest speed. I do ok With Aluminum but i can only take about .004" at a time on mild steel.
Any ideas? Thanks; Don

 

[brino]

The slowest speed may not be your friend!

You need to set your spindle rpm according to:
1) the tool material
2) the diameter of your tool
3) the material to be cut, and
4) the rigidity of the machine

For a HSS tool cutting aluminum, I'd aim around 110 sfpm.
For a HSS tool cutting mild steel, I'd aim around 80 sfpm.

There are various on line calculators, or see here:
http://www.hobby-machinist.com/threads/soft-jaws.55689/#post-460870

Also, if you can use the table locks for the direction you are not feeding then you can remove some motion of the table. For instance, if you are cutting with the X-feed, use the table locks for the y and z axis to help rigidity. If your mill does not have this feature you may be able to add it.

Please provide the tool material and diameter, maybe there will be more ideas.

-brino

 

[dontrinko]

Thanks; The mill is HSS 1/4" shank and cutting edge. I'm not sure what type of steel I am cutting . It is 1/8" thick. I got it at Menards. when i buy steel it is 1018.
the slowest speed on my unimat is about 500 rpm, The next fastest is around 750 rpm.
the Unimat has a 1/10th hp motor. Don

 

[brino]

the Unimat has a 1/10th hp motor. Don

Hi Don, that is a small motor....but let's see if we can help.......

For a 1/4" dia. cutter you'd want:
near 1222 RPM for cutting steel (80 SFP)
near 1681 RPM for cutting aluminum (100 SFPM)

Other things under your control:
-use sharp tools
-use cutting fluid (I like pipe threading fluid for steel and wd40 for aluminum)
-control your depth of cut (DOC)
-listen and feel what the machine is saying

Anything you can do to increase efficiency is very important with a small motor and possibly flexing machine.

Hope fully someone with the same/similar machine will comment on RPM and DOC they use.

-brino

 

[grzdomagala]

You may try "free cutting steel" for some parts - it's available only in bar form and (afair) not weldable but cuts very nicely.
I too have quite small and not very sturdy machine (proxxon bfb2000 with kt150 and bfwe40 spindle) - i often use diy fly cutters (up to 20mm working diameter) since the machine "chatter" destroys endmils very fast - regrinding flycutter costs 5 minutes, endmill costs 6 bucks...

 

[dontrinko]

Looks like my rpm is way to low. I can fix that easily by moving to different pulleys. I do control the depth of cut: I have a dial indicator setting on the gap of the motor mount. I have the mill in a collet adapter that holds it firm but it sticks out further than i like. (ER16 adapter, should be E16) i am bidding on the proper adapter now online. I could use my drill chuck , it is actually fairly good on runout. Thanks everyone for the ideas; Don

 

[dontrinko]

Set rpm to 1100 and did test cut with same steel. I was able to cut .011" easily. I probably could have done more but had other things to do. Don

 

[brino]

Excellent!

 

[bfd]

tou might try a roughing end mill. they come in 1/4" also carbide in that size will allow for faster rpm without burning up bill

 

[Wreck™Wreck]

Material and Material Condition should not be confused, material condition is often dictated by its method of manufacture, buying unknown material that is nominal 1018 steel is a crapshoot at best especially in sheet products.