Denker's Mini Mill PAGE


Home Built Mini Mill Information

My mill is a combination of purchased mini mill assemblies and other purchased and fabricated parts. The head assembly (R8) and column are standard mini mill with a purchased compound mill table mounted on a 1/2" thick steel base. Everything is greatly modified. The column does not rotate on the base like the standard machine, but is held vertical by .25" thick supports and a 4" webbed iron angle plate. Instead of the standard head support spring or gas support system, I am using a counterbalance. (far better) I went with a different table because I wanted something a bit heavier and .100" per rev. dials. I used a standard 5" x 8" PHASE II table and modified it. For the most part it came out very well but I would recommend using a large U-beam for a base instead of a flat plate. My plate required extra supports.

 

 

Modification Contents:

 Compound Table

 Counterbalance

 Low Speed Addition

 Table Power Feed

 Z-Axis Control (New)

 Other Additions & Changes

Home


Compound Table

The mill table I bought was a little on the ruff side. I paid about $70 for it and it showed. The acme screws had between .010" and .015" of backlash and the handles were too small. It came with the X-axis handle on the left so I switched it to the right side. To remove some of the backlash, I added thrust bearings and made new longer acme screw shafts to accommodate the extra length of the thrust bearing housing. (Also added length for a power feed unit) As long as I was doing that, I made new acme nut brackets too. Now the backlash is under .005". It would be better if I used better acme nuts or bought a 1/2-10 acme tap and made my own. I also had to add X and Y-axis lock handles (this table did not come with them) and added inch scales. Finally I replaced the 2.5" handles with 3.5" brass ones to get an easier feel. Overall this was a lot of work for a heavier duty table. Was it worth it? - I'm not sure. To get .100" per rev. feed, there are not a lot of low priced options out there.

Back to top

Home


Counterbalance

From what I have read and seen on the Internet, the mill head support systems used on the standard mini mills are not very good. I decided to go with a counterbalance system instead. I mounted a 4" pulley on top of the column and a 10" THOMSON linear bearing bar (surplus) on the back for the weights. I connected the head to the weights with a plastic covered steel cable. The motor controller box had to be mounted on the left side of the column. It works great but adds major weight to the machine.

Back to top

Home


Low Speed Addition

This is a big project that required a lot of machining and just as much engineering. It gives the machine a 0 to 700 RPM speed range with 1.5 times the output torque. It also bypasses the internal plastic gears. The motor is mounted on a position plate so it can be moved forward or back. To engage the low speed range, I move the motor to the rear position where it engages a different gear. This system reverses the spindle direction so a reverse switch must also be added. This is not a easy addition but it sure is worth it. I can now use bigger drills and mills and with the reverse switch I can use it for tapping without a big tap head. The housing is made of 1/2" thick aluminum plates layered 3 high and bolted and pinned together. It uses the same timing belt system as the low speed addition of my mini lathe but with a gear instead of the V-belt. I changed the gear on the motor from a 16-tooth to a 15-tooth so the higher speeds are now 0 to 1040 RPM and 0 to 2380 RPM.

This housing also has a spring-loaded spindle lock pin and a work lamp mounted to it.

Back to top

Home


Table Power Feed

This is not an easy project and required considerable engineering. The housing is a 3" x 3" x .125" thick square aluminum tube that encloses a SCR motor controller with the relays, gearing and bearings needed for the drive. I'm using a 30VDC motor that draws about 1 amp and has a motor overload protection circuit set at about 1.5 amps. It also has stop switches for adjustable position stops located behind the compound table. There is an engagement lever to engage the X-axis acme screw because a worm gear is used in the design and the X-axis cannot be moved by hand with the power feed engaged. The maximum feed rate of this system is about 8" per minute. A separate box located behind the mill houses a power transformer, 2 amp DC circuit breaker and 1 amp fuse for the unit.

Back to top

Home


Z-Axis Control:

I have found z-axis head control can be a little tricky for some operations. Because the hand and fine feed controls use a gear and rack, which has a bit of slop, operations like drilling out large holes, boring and vertical milling can be a problem. To make this easier I added a z-axis screw. Others have done this and I found it helpful too. For normal operation, I remove the two bolts from the screw head bracket and rotate it 180 to the back. (Shown just under the head locking lever) I am using a 1/2"-20 threaded rod so each turn moves the head 0.050". The purchased rod I used is not dimensionally accurate and is off by about 0.040" in 10 inches. I would have to make my own screw if this was not good enough in the future. With this now in place, I removed the old fine feed system.

Back to top

Home


Other Mill Additions & Changes:

 It is an absolute must to have a Z-axis indicator. This one uses an addition to the mill stop bracket to engage a 1" travel indicator mounted to the mill head. I have a 1" and 2" spacer that can be added when setting it up to get longer movements. (up to 4" total)

 In the above picture you can also see an added column chip guard. It is a thin rubber mat cut to about 5.5" x 12" with weight added on the bottom and mounted to the mill head. It's cut just long enough to protect the wear surfaces. As the head moves down, it folds in place.

 Another addition that is very nice at times is a Y-axis indicator. This takes the guesswork out of the backlash of the table. For less wear on the indicator, I only mount it when needed. (I also have a similar 2" X-axis indicator system - not shown.)

 

 I have a small air compressor in my shop and have air blow off brackets and nozzle mounted on the mill. I don't have an air lube system yet but plan on one in the future.

 

 In the first picture at the top of this page you can see lights that I have mounted to the mill. I have 3 of them (one under the mill head) and I'm not sure you can ever have enough.

 This is a chip containment box I have mounted on the compound table. It is easily removed with 6 thumbnuts when milling large parts or for long parts, ether side can be replaced with a shorter version. With it and the mills stock shield, I can contain over 95% of the metal chips in the box. It sure makes cleanup easier!

 

 This is my drawbar wrench and mallet. It was made from an old broken 3/8" ratcheting socket wrench and an 18mm socket. Also added was a 1 3/8" dia. plastic mallet end.

Back to top

Home


All pictures and content Copyright © 2007, 2008, 2009 David Denker. All Rights Reserved.

Last Revised: June 2009