Fine Tunning a Grizzly MiniMill

When I originally was thinking about a mill for milling jobs I had figured I needed something that was bigger than a Sherline but smaller than some of the popular mill/drill table models. I figured the Grizzly minimill would be perfect for the modeling work I wanted to do. I'm now finding out that a bigger mill would be nice to do some of that live steam work on, but I still need something to do the work on that the Sherline won't handle. I've already replaced the plastic gear once on the machine. I was thinking of going to the belt conversion that was written up in one of the metal working publications but have never got around to it. The portion of the site will document some of the changes I have made to the mill.

Changing from a 16TPI to a 20TPI lead screw

The grizzly MiniMill comes with 16TPI lead screws. One turn of the dial moves the table .063". So for 16 turns of the dial your table will travel 1.008". You could hold back .008" on the dial, but this gets complicated if you have to move several inches and plus some thousands. The dials are also confusing to read. Help has come in the form of a set of lead screws sold by Micro Mark for there minimill, which looks just like the Grizzly except that it's red. The conversion kit changes the 16TPI to a 20TPI lead screw with .050" dials. This conversion is easy to do. I hope the following explanation and pictures will get you motivated to do the same. It will make projects on the mill much easier to do.

	Getting at the lead screw is quite simple. Just remove the two screws on the end to the bracket holding the hand wheel. Loosen the gib screws and slide the table to the left. Careful it may be small but is still surprisingly heavy. This picture shows what you'll see once the table has been removed. Now its just a matter of picking up the lead screw and undoing the two nuts that hold the hand wheel to the lead screw and pulling off the hand wheel. A few gentle taps with a plastic hammer and the wheel pops right off. By the way, that piece of metal laying in the bottom of the turned over table is the gib key.
	This is what you'll get once everything is disassembled. The hand wheel, end bracket with the thrust bearing still in place, lead screw, lead screw nut, inside thrust bearing, the old dial and the key that keys the hand wheel to the lead screw. All comes apart quite easy. I used an arbor press to press out the lead screw from the thrust bearings, but a piece of wood and a few small hammer blows should work just as well. Take out the key first though.
	Here are the parts for the cross slide or "Y" axis. Now that the machine has all been disassembled I just need to wait for the new parts to arrive.
	When the new parts arrived I noticed that the table lead screw was a bit different. It was longer and had a slot milled in the end. This is for the power feed that Micro Mark offers to drive the table. A nice feature but a bit pricey for me at $149.95. The price also includes the inch feed screw.
	This picture shows the cross slid ("Y" axis) lead screw back in the machine. The allen wrench is on a set screw that is used to tighten the nut securely to the cross slide. Bring the table all the way toward you and snug the set screw down. Now crank the table all the way back to see if the lead screw binds. If it does then you'll have to reset the nut until there is either no bind or very little. You can also see two screw holes to the upper right just below the curved cut out for the table lead screw. These two screw holes hold the table nut in position and are tightened in a similar manner as the cross slide nut.
	After I had assembled the table lead screw back into the end bracket, mounted it to the table and adjusted the gibs I noticed a bind on one end of the travel. At first I thought it was the gibs. But after removing the table I discovered that the paint was rubbed off the bottom down the center of the table.
	A bit of black marker on the table nut revealed that the table was indeed rubbing on the nut.
	A bit of grinding took care of the interference problem. I needed to do this a few times before all the interference was removed.
	Everything has been adjusted and is working properly. The mill is back together and in better working condition than before. With those new lead screws milling jobs will now be much easier to do. Next project for the mill is a motor drive for the table.

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