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Mini-Mill - Ideas on Improving Low Speed Torque?

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gjmontll

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#1
I have an X2 Mini-Mill, with the LMS Belt Conversion (without it, I'd have stripped many plastic gears.) And I sometimes have a problem with slow speed cutting (for proper feet per minute) and inadequate torque. This typicaly occurs when using relatively large diameter tools on normal low-carbon steel, best example is when using 3" diameter slitting saws on steel ( hot or cold-rolled) or drill rod. Other times are flying cutting and large diameter boring with carbide cutters.
Per Machinery's Handbook, I should run in the 60 - 90 sfpm range -- this is only 76-102 rpm and way too slow for the Mini-Mill to have enough torque to avoid stalling.
Running with enough speed to avoid this is clearly damaging the saw blades. I've resorted to many very shallow passes ( 5 thou?) but forum comments typically suggest a slow, deep cut.
I've considered adding additional belts and pulleys between the motor and spindle for more speed reduction, or maybe making a geared reducer to insert somewhere in the drive train (ideally on top, integrated with the belts).
Or is there some simpler solution?
 

cmantunes

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#2
Or is there some simpler solution?
Carbide slitting saws. You can safely multiply that SFPM by 3 or 4 (that's what I do). Drawback is the price of carbide vs HSS. I tend to buy carbide slitting saws directly from China to avoid breaking the bank.
 

brino

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#3
I am not familiar with the X2 mini mill, but the typical solutions are the same regardless of the machine type.
However, they all come down to how difficult they are to implement on the given machine.

1) as you stated adding a counter-shaft with extra pulleys and belt to lower the speed
2) changing the motor to a lower RPM motor
3) adding a gear reducer, a 90-degree worm drive can reduce rpm a bunch in one step
4) changing the motor to a speed-controlled type, like a DC treadmill motor
5) depending on the depth of your required cuts, you could also use a smaller diameter slitting saw. the smaller diameter ones can be run faster for the same sfpm.

You do need to be careful with the larger diameter cutters, they can put a lot of force on a smaller mill.

-brino
 
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