Home Made Table Feed for SX3 Milling Machine

One of the first projects I did after purchasing a lathe (got the mill first) was to make a power table feed for the mill. So as usual, I scoured the internet and catalogs to see what I could steal from the current manufacturers of SX3 table feeds. First place to check is Grizzly, since they have all the schematics, specifications and instruction manuals for their products online. Grizzly does sell a table feed for this mill for about $275 clams. It looks like they use a DC motor with a motor controller with a maximum power output of 100 Watts. Their system also has limit switches that prevent over-travel of the table, preventing possible damage to machine components. The only 'bad' feature about the stock Grizzly table feed (aside from the $275) is that you cannot easily disengage the power feed from the lead screw without removing the entire table feed unit. The better home-made versions of the power feed that I could find on the internet used a sliding shaft that would allow engagement of the power feed only when desired. This allows the feed unit to be disengaged so that you could still use the hand wheel when you wanted to. Most of the home versions were kind of crappy. A lot of them used a windshield wiper motor and a wall transformer with no speed control what so ever. And they seemed to look about as well as they worked. Come on people, you have a milling machine and you can only make stuff that looks like it came from a scrap heap?

24 VDC Gear Head Motor

I went down to the ol' base-o-ment and pulled out a drive motor from snowbot. I got these motors on ebay a couple years back for about $10 each, it was a good deal. They run on 24 VDC, draw about 2 amps under load and rotate at 180 RPM. The only bad thing about them is the face mounting threads are metric, but I was able to find some outrageously priced metric screws at my local chinese junk dealer, ACE hardware. The output shaft on the motor is metric I’m sure, but it's about 5/16" diameter so let's just call it 5/16". 50 Watts is half the rated power of the Grizzly table feed, but since the motor was at 'no cost' I figured I'd give it a try and if it didn't work, I just put a bigger motor on there.

24 VDC Power Supply

For some reason I don't seem to have any good 24 VDC power supplies. I have a lot of those wall transformer guys but most are limited to about 1 amp. Because this thing was going to pushing my mill table and machine parts, I didn't want to risk underpowering an already possibly under capacity motor. So I found a deal at all-electronics, a favorite surplus electronics dealer of mine for a totally enclosed, fan-cooled, 24 VDC power supply with standard AC cord input, local power switch and a 4 amp capacity for only $25. What a deal, I bought it. This power supply is good for up to 100W, so again if the motor is too small I can easily upgrade and use the same power supply. The power supply is mounted to the bottom side of my work bench table-top. It's out of the way and I can easily switch it ON when I need it.

24 VDC Motor Speed Controller

Ok, here's where things got interesting. I needed a 24 VDC motor speed controller rated for at least 100 W (in case of upgrade) that was reversible and cheap. Well I found a bunch of similar ones with H bridges but I thought I wanted one with a real reverse/forward switch instead of just a single pot. It took me a while but I ended up on ebay of all places. I bought a 200W unit with reverse polarity relays, switch and potentiometer shipped directly from china for about $30. You just never know what you get until it shows up, but in this case I was impressed. The soldering joints looked good and it didn't stink too badly. The only sketchy thing was the IC's had all their markings sanded off. So either they wanted nobody to copy the IC chips (making replacing them difficult) or they used a batch of stolen, defective or otherwise non-ligite IC's to save a dime. But when I tried it out, heck it worked just fine! I mounted the speed controller in a project box I had previously purchased for a 'bat-detector', which, never worked anyways.

Mounting Hardware

Well I got all my junk together and made a design in ACAD for the whole thing. So really all I needed to do was mount a motor bracket to the milling machine with enough space between the two to accommodate the 'slide collar' that allows disengagement of the feed without removing the entire assembly. The slide collar slides up and down the motor shaft and a cross-shaft in the motor shaft transmits the rotation motion from the motor to the slide collar. The slide collar is then tabbed to fit into the milling table screw slot. It was tough getting the dimensions of the bolt patterns from the milling machine. I'm not too good at measurements. The motor bracket was made from 1/4" steel plate and welded together. I got this plate from the local steel supplier, Fausers.

Limit Switches

Well going through all the trouble of making limit switches sure is a lot of work. But since I was waiting for the boat from china that was carrying my motor speed controller I had nothing better to do. So I looked in the basement again and pulled out two identical limit switches, likely from microwave ovens plucked out of a dumpster somewhere. I made up a mounting bracket to place the limit switches in the same spot the grizzly system uses (thanks griz!). These switches are wired in series with the motor power so if they trip, all power to the motor is lost. Also from the griz system are two positionable spring loaded limit switch smackers. They're spring loaded so that when the limit switch gets hit at mach speed, there is some room for the table to keep moving before it rips the mounting bolts out of the limit switches. What a good idea, i thought so.

Power Mowing

I tried out the motor feed control with a fly cutter on some aluminum plate and the results were excellent. The speed range was certainly not too fast with good slow speed range control. I don't think faster would save me much, at least with this little milling machine. I also plowed through some plastic parts at full speed and that little gear head motor had no issue at all. I haven't used it much on steel parts but for aluminum and plastics it has worked well. I do wish I had mounted the motor control box on the bottom side of the motor so everything would be flush with the milling table instead of sticking above it.

Link to the initial design of the motorization.
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