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Power Z Conversion For PM45

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I have an early model PM 45 mill that has the manual hand crank for Z elevation. Since I just reorganized my shop and a toolbox is placed nearby, I'm going to attempt to convert it to powered elevation using a heavy duty gear motor that I've had for a long while.

I'm not 100% sure this will work to my satisfaction. The odds are maybe 70%... We'll see. I'll outline the design considerations as we go.

Here's some pictures and explanations...

Here's the mill with crank handle removed. I put a wrench on the shaft flat and roughly measured the torque needed to raise the head. Holding the wrench about 1 foot (little less actually) from the point of rotation, I measured about 8-10 lbs to move it. This was measured by setting weights on the wrench which is a little inaccurate. Anyhow, I'm assuming it needs 10 ft.lbs to keep it in motion.

IMG_20180505_084318.jpg


Here's a gear motor purchased at a surplus shop that I've had laying around for years. This motor is used in mobile-home campers to slide-out the extension walls and rooms from the sides of the campers. It's very heavy duty and purchased new, they cost over $300.

http://www.cshincorporated.com/rv-power-gear-slide-out-motor-pn-523900-k01531a300/
  • Speed 6 RPM @ 850 in-lbs, 25 Amps
  • 10 RPM @ 400 in-lbs, 13 Amps
  • 12 RPM (no load)
  • Voltage 12 DC
  • Torque 850 in-lbs
  • Holding Torque 500 in-lbs.
  • Rotation Reversible
  • Duty Intermittent
  • Enclosure TENV
  • Mount Four bolt face mount on 3.38" x 3.38"centers
  • Dual Shafts 3/4" diam. x 1-1/4" with 1/4" crosshole (no keyway)
  • Size 9-1/4" x 3-7/8" x 6-1/4"

IMG_20180505_100601.jpg

So... 400 in.lb is 33.33 ft.lb but, this is at 10 RPM. One full crank raises the head 1/8" so, it would take almost a minute to raise 1". -Too slow... Gears are needed!

With a 3:1 gear ratio, I'll only have 1/3 available torque, which happens to be 11.11 which is really darn close to the 10 ft.lbs I think is needed to move the head. With a 3:1 gear ratio, I'll get 30 RPM instead of 10. This means the head will raise 3.75 inches in 1 minute. That seems terrible but, it's not. Manually raising that head with the crank is a royal pain in the butt and is a very slow process. For the convenience of flicking a switch... I can live with slow.

A simple 2-gear solution immediately came to mind. For many, many years, I would dream-up ideas and just slap things together on the fly but not anymore. I no longer kludge things as I go. Time is too short and precious and I dislike getting 50% done only to find I'm boxed in a corner where my choices are ugly.

Here's a CAD model. The gear and shaft diameters truly represent the pitch circle. Given this, I can use CAD to take centerline measurements of the shafts and design an enclosure that will hold the gears at the correct spacing.

CrankMotorModel.JPG



In the model, the gear sizes represent 85 and 35 teeth (respectively). This is a 2.43:1 ratio, not quite the 3:1 ratio I was thinking about before. This is because I'm using scrap pieces of metal for the gear blanks, using-up existing metal in the junk pile. 2.43:1 will be a little slower but, will give a little more torque.

So... Toss out questions, comments and suggestions. I'm going to dig-around the junk pile for more stuff and think this over before I start cutting gears.

Ray
 

Comments

#2
At the last minute, upon doing some time trials of how long it take me to manually crank the machine, I settled on gear ratios of 32 and 85.

Here are the blanks, I just finished them before posting.

I'm going to use some Modulus 1 gear cutters which are the closed size profile for what I feel will do the job. I have Mod 1, Mod 2 and DP 16 sized gear cutting sets. Given the overall size I want these gears to be and give the scrap pieces laying around, Mod 1 was the way to go.

Let me know if you want to see the calculations for the gear blanks and a refresher on tooth calculations.

The round collar is mainly cosmetic and just holds the bearing in place that supports the shaft. I'll remove the collar before attaching the motor unit.
IMG_20180505_124758.jpg

IMG_20180505_124836.jpg

Ray
 
#3
I have an early model PM 45 mill that has the manual hand crank for Z elevation. Since I just reorganized my shop and a toolbox is placed nearby, I'm going to attempt to convert it to powered elevation using a heavy duty gear motor that I've had for a long while.

I'm not 100% sure this will work to my satisfaction. The odds are maybe 70%... We'll see. I'll outline the design considerations as we go.

Here's some pictures and explanations...

Here's the mill with crank handle removed. I put a wrench on the shaft flat and roughly measured the torque needed to raise the head. Holding the wrench about 1 foot (little less actually) from the point of rotation, I measured about 8-10 lbs to move it. This was measured by setting weights on the wrench which is a little inaccurate. Anyhow, I'm assuming it needs 10 ft.lbs to keep it in motion.

View attachment 266844


Here's a gear motor purchased at a surplus shop that I've had laying around for years. This motor is used in mobile-home campers to slide-out the extension walls and rooms from the sides of the campers. It's very heavy duty and purchased new, they cost over $300.

http://www.cshincorporated.com/rv-power-gear-slide-out-motor-pn-523900-k01531a300/
  • Speed 6 RPM @ 850 in-lbs, 25 Amps
  • 10 RPM @ 400 in-lbs, 13 Amps
  • 12 RPM (no load)
  • Voltage 12 DC
  • Torque 850 in-lbs
  • Holding Torque 500 in-lbs.
  • Rotation Reversible
  • Duty Intermittent
  • Enclosure TENV
  • Mount Four bolt face mount on 3.38" x 3.38"centers
  • Dual Shafts 3/4" diam. x 1-1/4" with 1/4" crosshole (no keyway)
  • Size 9-1/4" x 3-7/8" x 6-1/4"

View attachment 266845

So... 400 in.lb is 33.33 ft.lb but, this is at 10 RPM. One full crank raises the head 1/8" so, it would take almost a minute to raise 1". -Too slow... Gears are needed!

With a 3:1 gear ratio, I'll only have 1/3 available torque, which happens to be 11.11 which is really darn close to the 10 ft.lbs I think is needed to move the head. With a 3:1 gear ratio, I'll get 30 RPM instead of 10. This means the head will raise 3.75 inches in 1 minute. That seems terrible but, it's not. Manually raising that head with the crank is a royal pain in the butt and is a very slow process. For the convenience of flicking a switch... I can live with slow.

A simple 2-gear solution immediately came to mind. For many, many years, I would dream-up ideas and just slap things together on the fly but not anymore. I no longer kludge things as I go. Time is too short and precious and I dislike getting 50% done only to find I'm boxed in a corner where my choices are ugly.

Here's a CAD model. The gear and shaft diameters truly represent the pitch circle. Given this, I can use CAD to take centerline measurements of the shafts and design an enclosure that will hold the gears at the correct spacing.

View attachment 266850



In the model, the gear sizes represent 85 and 35 teeth (respectively). This is a 2.43:1 ratio, not quite the 3:1 ratio I was thinking about before. This is because I'm using scrap pieces of metal for the gear blanks, using-up existing metal in the junk pile. 2.43:1 will be a little slower but, will give a little more torque.

So... Toss out questions, comments and suggestions. I'm going to dig-around the junk pile for more stuff and think this over before I start cutting gears.

Ray
You are on the right track using an RV slideout motor. I did the same on my RF-30 mill a couple of years ago. These motors can move a slideout that weighs several hundred pounds so raising a milling machine head should be easy.

Here's a couple of pictures of my setup.

IMG_0300.JPG

IMG_0301.JPG
 
#4
You are on the right track using an RV slideout motor. I did the same on my RF-30 mill a couple of years ago. These motors can move a slideout that weighs several hundred pounds so raising a milling machine head should be easy.

Here's a couple of pictures of my setup.

View attachment 266897

View attachment 266898
Thanks... That's a good data point to be aware of. The model of gear motor I have seems to be common and the specs are impressive but still, there's always an element of surprise when you first slap something together.

Ray
 
#5
We have a little detour due to a surprise when cutting the gears. Actually, I got a double-whammy... For the gear teeth sizes I chose, one of them can't be cut with a 90:1 rotary table. 85 is not possible so I decided to go with 80 teeth because it needed the same hole-plate as the mating 32 tooth gear. -And of course, I either did not have, or cannot find, the plate with 64 holes which is needed for the 32 and 80 tooth gear.

So... How do you fix that?

Behold... 64 evenly spaced holes.
IMG_20180506_185312.jpg IMG_20180506_220854.jpg IMG_20180507_180146.jpg

Almost done. I need to drill the 3 holes in the middle. Later on when this project is over, I'll drill the other hole sets that belong on that plate. I think 62, 54 and 50 are missing. I'l get e'm all on there sooner or later even if I have to stagger them.

When I finish the 64 hole plate after dinner, I'll come-back and do a write-up of gear calculations and gear cutting.

Ray
 
#6
This came out nicely and it fits/works perfectly on the rotary table. Those 64 holes was a minor pain in the butt. All total, it took 2 hour to drill them. Would be a perfect job for CNC. I made 2 passes. Spot-drill followed by the drill. I took my time and approached each hole position with the same approach on the wheels. If I accidentally overshot, I would back up a good amount and re-approach always turning the hand wheels in the same direction for every hole. Doing this seems like overkill but, from past experience, I've learned this technique is effective when looking to drop multiple holes from a common datum.

It paid off. Using a couple pin gages, the hole spacing was spot checked in about 15 places and everything came-out surprisingly uniform. The variance on the factory plate was about the same as the new one.

IMG_20180507_210553.jpg

Ray
 
#7
I wanted to get one of those motors back when surplus center had them, but I snoozed and lost out.
 
#8
OK, gears are made (see link here: https://www.hobby-machinist.com/threads/cutting-gears-diametral.69653/#post-583860) so this motor attachment project can move on.

No big deal here, just cut a keyway into the gear motor shaft.
IMG_20180512_153852.jpg

Make a box to hold the gears. This 11 ga (.120") hot rolled. It was TIG'd together then rounded off. If this works I'll build side covers for it and paint it too.
IMG_20180512_191725.jpg

Preliminary layout of gears as a sanity check.
IMG_20180512_191959.jpg

Drop some holes as per the model.
IMG_20180512_204022.jpg

...and drop more holes. These are elongated so the motor can be positioned with the correct gear engagement.
IMG_20180512_210822.jpg

And so far, it looks like everything is lining up OK. I still need to drill/tap into that heavy plate. There are 3 holes around the shaft at the top but, they're only 4 or 5mm. There's going to be a lot torque placed on them so I want at least 1 more at the bottom. Also, I screwed-up and made the box too small. The plan called for it to be 6" x 4" x 2.4" and for whatever reason in the universe, I made it 5" x 4" x 2.4". That's why I welded a tab on the top. It's good enough and I'm not going to mess with it. It will serve as a constant reminder not to make stupid mistakes.
IMG_20180512_211904.jpg

None of the screws are tight but things will line-up nicely when everything is snugged-up.
IMG_20180512_212024.jpg

Almost there... We'll be testing this tomorrow if all goes well.

Ray
 
#9
FYI: After making shaft keys, getting everything aligned, bolts tightened and test-run with an automotive battery charger...

There's no flexing in the housing, the shafts are not splaying under torque and the motor does not seem to be straining. Best of all, the travel speed is about identical to what I can do cranking it manually. I ran it the full travel up & down twice in a row (a very uncommon scenario) and the motor warmed-up only a few degrees over room temperature.

So far, so good -and I should have done this about 6-7 years ago when I bought this mill.

The project is not over... The search is on for a dedicated 12v power supply that can source about 20 amps. Then of course, finishing it off with full enclosure, paint, reversing switch etc..

BTW: No, the box is not crooked... The cheap phone camera gives fish-eye lens distortion to anything close-up.

IMG_20180513_083502.jpg

Ray
 
#10
Looking good! Thanks also for the gear cutting lesson which sure seemed to shed some light on that topic for me at least. :encourage:
 
#11
Makes me want to find supplies to do this to my grizzly.
 
#12
So... I ordered the 40A version of this 12V power supply and I happen to have a left-over PWM speed controller from another project. I'm guessing this power supply functions as a current source so the speed controller should tame it down if needed.

https://www.ebay.com/itm/Universal-...var=422931826550&_trksid=p2057872.m2749.l2649

That power supply says it's for LED strip lights. Here's a question for y'a. Who in hell is going to power 480 Watts of LED lights? Somebody is trolling for UFOs? What am I missing here?

Anyhow, I wanted to make sure the gears were meshing properly because it's hard to adjust that mechanism due to visibility. Everything sounded OK and looked good. No signs of grinding etc... I ran a strip of writing paper through there to make sure there was a good impression without shredding at the root or tips of the addendum. It seems OK. I'll have to do it over once this is finalized.

We all know the dangers of gears but I gotta tell you, watching that paper get slowly churned through those teeth... Oh, you could make somebody talk with that setup.

IMG_20180513_112431.jpg

Oh, Redmech: Check Surplus Center for those motors. The show-up there once in blue moon. I think mine cost around 75 bucks about 8 years ago. https://www.surpluscenter.com/Elect...ors/DC-Gearmotors/?page_no=1&page_length=9999


Ray
 
#13
BTW: The power supply, reversing switch and on/off toggle switch showed-up today. No sign of the enclosure yet but I still wired it for a test run. The power supply is amazingly good. I bought one rated for 40 Amps because it wasn't very expensive at all. It has a little pot for voltage adjustment. I set it for 12.50 volts under no load. Under full load moving the head up it keeps the voltage rock solid at 12.50 and can moves the head up without straining at all.

https://www.ebay.com/itm/Universal-...var=422931826550&_trksid=p2057872.m2749.l2649

Just waiting on the enclosure and this project is done.

PowerSupply.jpg

Ray
 
#14
I am curios to see how slow you can go and still move the head. With that setup.
 
#15
I am curios to see how slow you can go and still move the head. With that setup.
Pretty darn slow.

Since this is not fully setup with inline fuses, I only did limited testing with 15 second intervals when testing at low voltage. At the lowest voltage (10.4V), it was 1.2 IPM (ballpark). The head moved steadily and it was not balking or straining.

At 12 V the motor is supposed to spin 10 RPM. The gears were 80:30 which is 2.6666 ratio x 10, divided by 8 (Z leadscrew is 8 TPI) so, it should go 3.333 IPM. I'm setting the supply at 12.5 V and measured 3.5 IPM with consistent results on 3 tests. This worked out well and is right in the ballpark of what was hoped for. The velocity is essentially the same going either up or down.

The max voltage on the power supply is 15.5 V. I do not plan to test it at that voltage.

BTW, I have it wired with an On/Off toggle switch, a polarity reversing switch, and a debounced "momentary on" toggle switch. Giving it a quick "blip" on the toggle switch, at 12.5 volts, it consistently moves the head 7 thou -same distance either up or down. When transitioning from up to down (or down to up) it consistently displayed 3 thou total movement (i.e. 4 thou backlash).

During normal operation at 12.5V, when the switch is released, it has no carry-on momentum; that is, as soon as that switch is released, it probably travels about 7 thou inch before coming to a stop. This is expected since it's an ACME screw and not a ball screw.

Ray
 
#16
Sounds like should be able to bore with it then. I have the G0704. I need to find one of those motors.
 
#17
Sounds like should be able to bore with it then. I have the G0704. I need to find one of those motors.
The speeds line-up so you should be able to pull it off. Be aware, that particular motor is rated for intermittent use so, I wouldn't try to do many pieces in a row that take a long time to finish. Also, the motor was designed to run at 12 V nominal and was intended for use in mobile home campers. Automotive and RV batteries are typically 13.3 Volts (despite being called 12 V batteries) so, things will run with slightly lower amperage. Since power is conserved, running the motor at lower voltage causes a corresponding increase in current. With my limited experience with this motor, I don't know how it will react to longer-term operation at lower voltages. At normal voltages, the motor easily moves the head up & down and a PM 45 head probably weighs 2x as much as the 0704. Doing that at low voltage would heat it up for sure -which is why I would not do the experiment without fuses in place.

Not trying to be a nay-sayer... Just don't want you pay good $$$ and accidentally burn the motor up. If I were in your shoes, I would look around for some kind of stepper motor and a simple speed controller kit. Maybe there's an Arduino-based kid that can do this out of the box.


Ray
 
#18
Although “power is conserved,” that does not mean a motor operates at only a given power level. Take for example a simple brushed DC motor, which has a certain winding resistance. With a lower drive frequency, there is less current in the winding. Power is lower than at a higher voltage. In that example, power is V^2/R.
 
#19
The power supply shown is a straight-up DC regulated supply not a synthetic PWM DC drive. My comment about conservation was with respect to the parts used in this project. In this case, operating at increasingly lower voltage will increase current to the max the motor can draw. I did in-fact run it at low volts for several brief periods and I could feel the 12ga wires warming up more-so than at 12.5 V.
 
Last edited:
#20
The power supply shown is a straight-up DC regulated supply not a synthetic PWM DC drive. ... In this case, operating at increasingly lower voltage will increase current to the max the motor can draw. I did in-fact run it at low volts for several brief periods and I could feel the 12ga wires warming up more-so than at 12.5 V.
Not sure what relevance the power supply has to motor current. Also not sure what you mean by synthetic PWM DC drive; your power supply is a switch-mode power supply, which uses PWM to control voltage. But that's beside the point.

I don't believe there are many logical explanations for the motor drawing more current at a lower drive voltage, unless the load conditions on the motor were different. If you used a very low PWM frequency to drop the voltage, then current would contribute to heating.
 
#21
Not sure what relevance the power supply has to motor current. Also not sure what you mean by synthetic PWM DC drive; your power supply is a switch-mode power supply, which uses PWM to control voltage. But that's beside the point.

I don't believe there are many logical explanations for the motor drawing more current at a lower drive voltage, unless the load conditions on the motor were different. If you used a very low PWM frequency to drop the voltage, then current would contribute to heating.
Here's a good, old-fashioned .001 Ohm shunt resistor in series with the supply leads to the motor. I'm reading DC voltage across the shunt so the current will be the voltage reading / 0.001. It reads 6 mV (i.e 6 Amps) at low volts and 4.4 (i.e. 4.4 Amps) when set at 13.3 V. In all complete honesty, the 4.4 picture was usually showing 4.9 making the current just under 5 amps but when I snapped the picture, it grabbed 4.4. It was kinda hard to hold the leads and snap the picture at the same time.

FWIW, I observed similar behavior when playing around with one of these little gear motors....

https://www.ebay.com/itm/12V-3RPM-T...2233342920?epid=706769864&hash=item465e82d3c8


IMG_20180523_170446.jpg IMG_20180523_170924.jpg IMG_20180523_171001.jpg
Ray
 
#22
Thanks for the follow up. Makes no sense to me.
 
#23
Thanks for the follow up. Makes no sense to me.
Well, what now makes sense to me, is that I purchased WAY more power supply than what was needed. The specs on that motor were showing levels of 25A at max torque and 13A at 400in-lb. I did some measurements and came-up with a torque measurement at the crank handle. I was leery of the measurement technique and I inflated the estimate -a little bit too much. So, here I am thinking I needed a miniature welding unit to drive this thing and it turns out I bought 6 times more PS than necessary. On the flip side, the difference in price was about 12 bucks so... oh well....

Ray
 
#24
Always nice to see your work Ray. Thanks for posting!
 
#25
It was timely that I found this post. I am wanting to add power Z to my PM-45.
Dan Coleman
 
#26
That is a good mod and will pay off the first time you have to go from top to bottom and back again, cranking gets monotonous. Looks like a nice job on the gears.
 
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