12v Drill hacked to powerfeed for Mini Mill

[TroyO]

Not a completed project... as a matter of fact it's just in the "Hmmm, I wonder....." stage. I already have a PC power supply hooked to my mill as an "Accessory supply" (Lights, maybe a coolant pump, power feed etc.)

I finally got to take a closer look, and see what I have that may work for the power feed.

The "doner" is a 12V Ryobi cordless drill. I took it apart and it looks like there's some mighty usefull bits in there. The motor, gear drive and clutch are all one assembly. (Cylindrical, about 1.25 diameter.) I got the chuck off, the output shaft is threaded outside with what looks like maybe a 3/8" regular thread and tapped left hand threads on the inside. I don't know if the threads are metric or Imperial. (Yet)

Mounting it should be dead easy.

Electrically.... some pleasant surprises. I think the motor controller can be hacked. It may take some fancy soldering, but the main circuit board has what is clearly a potentiometer "strip" on the trigger that I'm pretty sure I can isolate and replace with an outboard potentiometer. The Fwd/Rev switch is a seperate unit from the controller and can be easily replaced with a regular triple throw switch.

I will take some pics next time I get to work on it and post them up, along with thoughts and how I manage (*if* I manage) to hack the speed control. I am pleasantly surprised by what I've seen in there... it looks like it may be easy to use not only the powertrain but even the speed controller too! I kind of figured it would be so proprietary there would be no chance of salvaging that part. It's obviously rated for it, and it's nice and small too.

This may end up being something like the $10 powerfeed... since the drill was a toss away.

 

[T70MkIII]

Looking forward to seeing your progress on this one, Troy.

I've been thinking about an x-powerfeed for a while. I think I have an old 12v model train controller somewhere, and I'm sure I have a defuct cordless drill or electric window motor lying around.

 

[itowbig]

looking forward for some really great pics yup yup :bow:

 

[TroyO]

Consider me prodded... well, a little anyway. My parents are coming in to visit next week, wife has had me cleaning and scrubbing, LOL. Maybe I can really dive in on it after next week.

Anyway... here's a couple of pics to get started. The body of the motor measured 1.45"

It's NOT a resistive trace like I thought it was. It's segmented on one side. Not a deal killer... actually in some ways it may be easier. From what I can see, there are 6 traces, each presumably activate a different speed. So, it won't be infinitley variable but it will have 7 speeds (Including stop, that is.)

I'm going to order one of these to run it...

http://www.mouser.com/ProductDetail...=sGAEpiMZZMvNbjZ2WlReYnqYHrQfuERsygueEKa171c=

It's a 7 postion rotary switch, "shorting" type. That, a double pole double throw switch for motor reversing and I think the electronics will be sorted.

Reversing switch I'm looking at is here:
http://www.mouser.com/ProductDetail...=sGAEpiMZZMvudeGI7i40XN5W0OOvRIfVYTvsRTE5jYs=

 

[fourjc]

I like your switch... I done this a few months ago and mounted the trigger in a box then made a rotary cam that depressed the switch for speed control... your method is much better.
I did not put a reverse on mine, figured that I will never need to reverse feed. It works fine but now I am thinking the reverse might be practical.
I had an electric clutch from an old copy machine, runs on 12 to 24 volts, I use this to turn the feed on and off without touching the speed (trigger in my case). I do have more pictures if interested.

 

[TroyO]

I'm picking this project back up again. Well, starting to anyway.

I gave up on hacking the original controller. I remain convinced it *could* be done the way I intended. I should have taken more care in taking it apart however. Inside the plastic casing were metal clips that connected various points on the board. The problem is they fell out when I cracked the plastic casing open and I wasn't able to figure out where they belonged, LOL.

So, I went the easy route and just bought a motor controller. I got this one from Ebay, just over $20 shipped. http://cgi.ebay.com/12V-15A-DC-Moto...546?pt=LH_DefaultDomain_0&hash=item3cb455fb5a

Yep... easy beat cheap this time.

It works just dandy, and I figured out a way to short the pot so I can use a momentary switch to kick it in to full speed mode. (Rapid). Plenty of torque even at low speeds.

So, here follows the stream-of-consciousness brainstorming session... LOL.

Controls:

1) Main power... probably one of those "Fighter pilot" flip switches as a pseudo emergency stop.
2) An indicator light... I will forget it is on.
3) Direction. Left/right.
4) Speed dial.
5) Go baby GO! (Rapid)

Hmm, anything else that would be handy?

I'm also debating whether I want the controls on the powerfeed unit, on the mill head or maybe even a pendant? Hmmm... nah, I have enough crap hanging out on my mill bench, pendant would just be something else to get tangled in.

Mechanical:
I have an extra table end like goes on the handwheel side. I got it once upon a time to see if I could work the bearing arrangement in to the Y axis. Turns out that wasn't very feasible, but it was only $6 and I got it shipped with some other stuff from Grizzly so the total wasn't much more.

18 P8689018 Y-AXIS BEARING SEAT $6.00
(Although it's really the X axis bearing seat.)

I'm thinking/hoping I can bolt that to the other side of the table as a bushing/mounting block for this thing. If it works out I will probably try drilling 2 hole "pockets" to mount 2 round stock rails in there as a slide for the motor. Then the motor can slide in/out on rails and just engage the split end on the leadscrew. Hmmm, add a spring and a cam and it may really be just that easy? Mounting the motor should be pretty straight forward... it has two screws holding the clutch mechanism in place already. Simply remove and re-assemble after passing the screws through a mounting plate.

Hmm, I will need a solid table stop as well to overcome the clutch... right now the X can just screw off the end of the leadscrew. The table cap may fix that issue, though.... matter of fact I’m pretty sure it does.

Finally... I’d love to get it to sit flush with, or slightly under the top of the table. That way I can throw something long on there without interference.

OK... stream done... for the moment, LOL.

(Edit.. Not counting what was on hand and and not otherwise being used the total is now: $27
$21 Motor control
$6 DPDT switch
)

 

[TroyO]

I putzed with the design a bit today. The extra end cap at least helped me realize something.... the leadscrew is offset about 1/8th from the center. So, I could maybe machine the outside surface flat, then flip it over and ount it backwards... but by that time I might as well just go ahead and make a fresh one.

I used a method I have had luck with before, but haven't seen mentioned. I scanned the existing end cap and created a B/W JPG from it. After a bit of cleanup it looks like Pic 1.

Then, I imported the JPG in to Inkscape, which is a freeware vector graphics app. Using the "Trace bitmap" tool I was able to then convert the shape into vector lines and edit them for some cleanup. Once it is a vector graphis it is very easy to scale/tweak/manipulate it. The overall size was way off after tracing, but by simply keeping the hight and width locked to the same ratio I was able to easily scale it back to match exactly.

And example of that is the CleanedUp.pdf. If I print that out from Inkscape I get a dead on 1/1 match of my end cap. Within a few thou for sure. It also is super handy for "curvy things" that are hard to measure. (Well, for me anyway.)

What good will that do ya? Well, now I can layout my part using the inkscape tools. It lets you place down to .0001 and although it's not the most advanced CAD type thing going... it's free and comparatively easy to use.

Now I have the layout... I can print it out as a reference, OR... glue it straight to the stock and work from that. (Depending on required accuracy.)

My untested and NOT reality checked end cap is in the endcap.pdf file.

(Edit... Grrr, not sure why but it thinks there is an inline image... there isn't. Just the 3 attachments. I also just updated the endcap pdf, found a couple of mistakes. there's probably more.. LOL.)

(Edit 2... got it, I had the wrong extension on it.)

View attachment CleanedUp.pdf

View attachment EndCap.pdf

 

[TroyO]

The first version didn't pass the reality check. I guestimated the size of the drill end at 2.0. Ends up it was 2.25".

So, I changed to (2) 1/2" support rails, still should be plenty. Anyway, here's the current revision of the mounting plate. I still have a slide plate and maybe a rear support to do.

(Edit... PDF didn't show text, fixed it.)



View attachment EndCap2.pdf

 

[TroyO]

Made some progress yesterday... got the mounting plate and the motor mount done. I need to update the plans.. LOL, no plan ever survives contact with the project, does it?

I used 3/8" AL plate, 4" X something. The basic dimensions in the plan were fine, I just made some changes so I could add a flip down lever to keep it disengaged.

So, motor mounting is sorted and so are the slides and the lever mechanism to disengage the leadscrew. That worked pretty well, actually. Now to make the adapter between the leadscrew and the motor, and make up the enclosure for it.

I'm kind of waffling about the best way to make the enclosure. Maybe I will knock up a quick bending brake and just bend it out of some sheet steel. The other idea was to use some angle iron and use that on the 4 corners and just cover the rest with flat plates. As yet undecided.

 

[mardtrp]

Here's another "useless" bit of info re the 12 volt motor out of that drill.

The early version of this saw had a 12 volt motor fitted and when you bought the saw you had to buy the step down power pack to go with it. Now being only 12 volt, it soon let out the magic smoke, so for a replacement motor it would have been cheaper to just go and buy a brand new saw.

This is where this motor from the chuck away drill comes into it's own, it's the exact same motor, even got the same numbers stamped on it. A bit of mucking about and bingo, the saws like a bought one again.
I can buy these "second hand thrown away drills" from the recycle centre at the local tip for 5 bucks, good value, eh.

http://www.proxxon.com/us/html/37006.html

This latest version of the saw, has a 110 or 240 volt motor fitted, they had been down the path of replacement motors for to long, so changed it to something better.

 

[TroyO]

I made some more progress. First, I made a adapter from the drill spindle to the leadscrew. I had a really good day running the lathe and managed to get a decent surface finish and all of the bores the right size. Unfortunatly I also made it precisely the wrong length while I was at it. Grrr... LOL. ??? So anyway, that is shelved for a while (Until I feel like repeating my steps... which will doubtless not work as well next time, LOL.)

So, I moved on to bending a sheet metal "Box" for it. I had access to a bending brake but no experience using it so it's mostly close-ish. It's off about a 16th one one side, so I epoxied a metal strip to it to make up the difference. Not ideal, but it will get the job done.

I'm debating how pretty I want to make it.... thinking I might skim it with some bondo and actually paint it up.

I got my control panel laid up in a pattern I think will clear everything. I'm using the attached graphic for that. I ended up with a pretty decent open space on the graphic so I threw in a chart I thought would be handy.

Anyway... I will probably get some work done on it this weekend, and will take some pics while i am at it.

 

[TroyO]

I made some progress but I haven't taken pics yet... sometime this week I'm sure.

I did run in to a problem, and now that I'm (fairly) sure I have it figured out I figured I would write it up.
It was an electronics puzzle. The potentiometer was set up in "The usual" fashion on that Ebay control. (3 leads, GND/Wiper/Positive 5V) I really wanted to have a "Go Baby Go!" switch that engaged full rapid while you held it down. Some futzing around with the circuit and I realized that by shorting the wiper to the +5V it would wind up the motor. Cool! The problem was, it wouldn't work when the speed was set below about 1/4 turn on the POT. I finally figured out why.... when the POT was turned "off" or low, what I was actually doing was shorting the +5V to the wiper, which in turn was at (or almost at) GND... Essentially shorting the GND and +5V leads together.

Not good. Luckily I didn't blow the controller in the process.
Not wanting to run it that way, or liking the "Has to be on somewhat" for the GBG switch to work, I starting thinking about other answers. To that end, I tried "Hot wiring" the positive lead to the motor.... which had no effect. Apparently the controller is PWM controlling the ground lead. Great! So I then jumper the GND to the negative lead of the motor and sure enough WHIIIIRRR!

Hmmm, problem though.... if I do that from a dead stop it overloads that 10A power supply and it shuts down. By running the motor a little first, then jumping the ground it was fine and went happily up to full speed.

Diagnosis: Power supply can't handle the rush current of the motor from a dead stop. I can however run the motor power from a dead stop through the PWM controller and not overload, presumably because the controller limits to 15A and that is within the surge capability of the power supply.

Re-think and consider the problem and it hits me... what I really need to do is get 5V to the wiper lead without shorting to GND in the process. Thinking back to my somewhat rusty electronics I starting thinking about pullup/pulldown resistors.

The potentiometer is acting as a voltage divider…. But what if I simply disconnect the negative lead to the POT with a momentary switch? That *should* give what is essentially infinite resistance to GND. Infinite Resistance to GND divided by anything the pot has between the +5v and the Wiper will always rise to VCC… in this case 5V. And off the motor goes whirring away……

I will need to replace my momentary switch with a NC (Normally Closed) instead of a NO (Normally Open) switch, but other than that it should give me a perfect full-speed override switch.

I’m mostly almost kinda sure it will work, LOL. If it does I will post up a crap-o-cap schematic for it, maybe it will be of use to someone some day.

 

[Troutsqueezer]

This is kind of hard to follow without a schematic of some sort. If you remove the pot's connection to ground, the wiper voltage will rise to 5 volts as long as there is no load on the wiper. If there is any current being pulled through the wiper circuit, the pot will drop voltage across the wiper/5V supply terminals proportional to the amount of current flowing through the wiper. Might still work, hard to tell without circuit details though.

 

[TroyO]

To an extent I am flying blind... I don't have a schematic for the motor controller. I probably could go back and reverse engineer the board, BUT... the chip number has been obscured on the motor control IC.

I do suspect that the wiper input is high resistance since it is going to an IC though, so current *should* be minimal?

I attached a "Crap -o-Cad" version of what I am planning in regards to the rapid switch. It's easy enough to test it tonight when I get home. I will post a complete wiring guide when the dust settles. It has a directional switch with a diode to protect the controller, a main power switch and of course the Rapid function (if it works).

If it doesn't work, the next idea is a big fatty capacitor on the 12V input and going back to the high-current grounding of the Negative motor lead. The hope being that the capacitor would supply some of the surge current and allow the power supply to cope. (4700 uF, the biggest Rat Shack had.) I would really rather handle it on the "Low power side" of the motor controller though.

Last resort would just be a bigger power supply.... computer supplies are cheap and easily hackable. This one just fits so well, though!

 

[TroyO]

Whooo hoooo! That did indeed work exactly as expected.

I figured out why going through the controller keeps the power supply from overloading.... it has a "soft start" feature built in. It sounds like it goes through two stages. (WhiiiiiiiiiiIIIIIIIIIIIRRRR)

Now, the next question.... I was playing around with "trimming" the potentiometer by adding in some series resistors on the ground side. That works well, and I can pick the minimum speed by choosing various resistors. (As it comes, I had to turn it up by about 30% before the motor started turning.)

This one is more of a functional question.... do I want to set a minimum speed and use my directional control to turn it "off" or have the thing stop when I turn the speed knob all the way down? I'm kind of leaning towards the former... set minimum to a slow crawl and use the directional switch for "Off". It seems less likely to walk away from it while leaving the motor "humming" but not going anywhere.

I don't know how commercial units work... anyone have thoughs on the best approach?

 

[Troutsqueezer]

While I don't have a power feed on my mini mill, I've thought about scenarios for which I would use one. It seems to me that if one has to power feed at a slow crawl, there are reasons for it. Either the bite being taken by the end mill is fairly large or care must be taken because the bit is approaching some end point of the cut. There may be other reasons for going slow but for either of these, I think I would rather move the table by hand, getting a better feel for how the rubber meets the road, so to speak.

My thought has always been that the power feed comes in most handy for those occasions when I have to traverse back and forth many times over a long distance because of the size of the work piece and the ol' arm with bursitis or tennis elbow is getting tired. In these instances, I would move the table at a fast clip.

My take on it then, is to not worry about slow speed.

 

[TroyO]

I can see using it to feed instead of hand cranking... most commonly at some medium/moderate speed. The "Rapid" or "Go Baby Go" is for the rapid transit to and fro, the potentiometer is used to range it in between. The usual operation I see is as follows:

1) "Air cut" some distance and set the speed control to whatever makes sense for the material.
2) Position for a cut
3) Start the auto-feed in the direction you want and make a pass.
4) When the pass is clear, reverse the direction and hit the rapid button to get back to point 2).

I think the motor driven feed will be more consistant than I am by hand, possibly giving a better surface finish.

I'm now waffling the other way on whether the speed knob should range from stop-full or slow-full. No matter what speed I set as the minimum, there will always be some reason I want to go slower at some point (Not sure why, it just seems to work that way... no matter what I choose I always seem to find myself wishing I had slower/faster/longer/shorter available after I pick, LOL) so by picking "stop" I'm only limited by the minimum torque/speed ratio allowed by the motor controller and motor combination.

 

[DaveH]

As TroyO came to my rescue, then perhaps you won't mind if I mention the following. One of the most difficult tasks in milling is turning the handle slowly for any time longer than 5 minutes. It becomes exceedingly tedious. When using small mills below 3mm dia your feed will have to be slow and steady or they will just break.

Dave

 

[TroyO]

Well, she is done!

I could go back and finish the plans, if someone is interested. It started with a plan, and I ended up kind of winging it, LOL.

Pics of the last steps, and here is a video.

[ame]http://www.youtube.com/watch?v=VL4ltA3rlio[/ame]

 

[chucketn]

Nice job, TroyO. Very professional in looks and action. I'm going to have to go back through the thread and make note so I can copy!

Chuck in E. TN