Currently doing some upgrades to my IH mill, moving to a ethernet Smooth Stepper and a break out board with more inputs. I’ve already built a fairly nice console using modbus and hard switches and I have to say it’s awesome. I should have built it years ago. One other improvement I did sometime back was to go with a solid state hard drive along with about twice the memory my previous pc had and a video card with it’s own memory.

I’ve just finished bench testing the new electronics this week and planning on having the mill back up and running next week. Next on the list of upgrades is a new spindle. I have an R8 now and bought an ntmb30 and am going to make a new spindle housing to use 2 angular contact bearing at the lower end and get away from the single tapered roller there. Upper will be a deep groove ball bearing. I'd like to rework the spindle to accept a BT30 gripper, but if I need to, I’m prepared to run a threaded draw bar for a while so I can use my collection of BT30 tool holders and pre-setter.

I have a 3 phase motor for the spindle that I’d planned on adding, the vfd for it is in the cabinet now. And regardless of which way I go, there will be a new spindle motor up there in the near future. Originally I had planned on going with the 2 position belt drive solution so many of you guys have done and in the past I got into some discussions on them. Then I started liking a single position belt drive and over speeding the motor some to get the higher rpm. In that case, the pulleys would be a reduction to increase the motors torque.

But for the past two years or more, I’ve found myself milling more steel that anything else. And that has stalled out my desire for the belt drive. A close second has been acetal, then aluminum. Lots of the steel is tool steel that ends up getting heat treated, so the need for a higher spindle rpm just hasn’t been there. But I will admit the stock 1600 rpm is a bit slow lots of times even in steel. The higher spindle rpm is the main thing that the belt drives gives the mill, but once converted, the original gears are gone. So there’s a huge loss of torque.

I’ve not done much thinking of just what the gear ratios in the standard mill head are, but I know they are steep in some cases. I know that the increased torque from the gearing can be replicated by more horse power. The commercial mills I've checked out have that larger horse power nowadays and I know they work well in either media. But most of those start at 7.5 hp and go way up from that. So they start with lots more torque than the 3 hp 4 pole motor I have on hand. If my thinking is correct, HAAS uses a 1:1 pulley ratio and runs only one set of pulleys (but way more horse power).

So I got a question for you guys that have made that conversion. How does your belt drives do when cutting steel? Do you have to take smaller doc’s and step overs to be able to run them vs when you had the stock gearing? I'm believing most of you used either a 2 hp or 3 hp motor, do you find that adequate with the belt drives you've done? What would you do differently if you were to do it all over? I don't see my machining projects changing much if any for the next couple of years at least, so I need to make changes that help me do what I do. Not hinder me. I want the cnc programs to take control of the spindle and that mostly means I should get rid of the gears. But I'm a bit afraid to. I'm ok with changing my machining tactics if things will work well enough, but there's not that much a guy can change when he's drilling a 1/2" or larger hole in steel. I got no worries on lots of the lighter stuff I do and running smaller end mills, the boring head, fly cutter and even the face mill, but I do with those that seem to me to require quite a bit of torque.

Thanks in advance for your input
Bob