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My DIY power drawbar for the PM 940 CNC VS. No air needed.

rodjava

Steel
Registered Member
#1
Take a look at my DIY power drawbar for the PM 940 CNC VS. I already had a Milwaukee right angle impact tool which I used for the drawbar. I can get quite a few tool changes on a single charge. There are two speeds and I only use the slow speed for now. This is my first prototype for this drawbar. It seems to be working just fine. I like it because it doesn't need an air compressor. It was fast and cheap to make. I can still use the impact tool be loosening up 2 set screws.

Rod in San Francisco
 

cut2cut

Active Member
Active Member
#3
Take a look at my DIY power drawbar for the PM 940 CNC VS. I already had a Milwaukee right angle impact tool which I used for the drawbar. I can get quite a few tool changes on a single charge. There are two speeds and I only use the slow speed for now. This is my first prototype for this drawbar. It seems to be working just fine. I like it because it doesn't need an air compressor. It was fast and cheap to make. I can still use the impact tool be loosening up 2 set screws.

Rod in San Francisco
This is really cool Rod!
I really don't want to run an air compressor due to the noise but really want a power drawbar.

Does the Milwaukee have a clutch to adjust so it won't over tighten or are you just doing it by "feel" ?

Jake
 

Bob Korves

H-M Supporter - Premium Content
H-M Supporter-Premium
#5
Nice job, Rod! I am still waiting for a quick change solution that does not annoy the neighbors. I can run my mill until late in the evening, but I think an air compressor and/or impact wrench takes things beyond what is neighborly...
 

Billh51

H-M Supporter - Premium Content
H-M Supporter-Premium
#6
Rod,
Nice idea and seems to work quite well. I may do something similar for my mill, Bridgeport clone. I have seen a lot of other ones using an air impact but like yours because I don't have to fire up a 5 HP compressor. It seems like such a waste to run if that's all you need it for. Kudos man.
 

rodjava

Steel
Registered Member
#7
Thanks everyone who chimed in. I'm glad you like the idea.

Knowing how much to torque is a matter of touch and feel on the trigger. When I manually tightened for a tool change with a wrench, it only
took a 1/2 a turn to torque it just right. The body of this Milwaukee impact can also be turned upside down if you wanted the trigger on the top for a more comfortable grip.
I'm not that tall, so for me the trigger feels right to be on the bottom. I will likely epoxy something on both sides of the forward and reverse control switch to make it easier and faster
to make contact without having to look for it. Right now the control switch is flush to the body and you have to make an effort to locate it to push it in.

I already invested a lot of money in the Milwaukee M18 tool line, so it made sense to me to use something I already have.
 

jbolt

Active User
H-M Supporter-Premium
#8
Nice job, Rod! I am still waiting for a quick change solution that does not annoy the neighbors. I can run my mill until late in the evening, but I think an air compressor and/or impact wrench takes things beyond what is neighborly...
I did something similar on my PM-932D using a corded electric impact wrench. It is not loud at all.

It turned out to be a little more work that I expected since I had to turn a new nose piece to mount it but worth it.

http://www.hobby-machinist.com/threads/electric-power-drawbar.57423/
 

jbolt

Active User
H-M Supporter-Premium
#10
Jay, Nice work on your drawbar!
Rod in San Francisco
Thanks Rod,

I like your idea of the right angle cordless tool. The cordless drivers are nice and compact. Keeps it simple.

I don't have (or need) a cordless impact driver so I looked for alternatives rather than investing in a cordless system. I'm still working on wearing out the old 18v NiCad cordless tools left over from my construction business.

The corded driver was $23 shipped from fleabay so it was a no brainier to explore if it was feasible to use.
 

rodjava

Steel
Registered Member
#11
Thanks Rod,

I like your idea of the right angle cordless tool. The cordless drivers are nice and compact. Keeps it simple.

I don't have (or need) a cordless impact driver so I looked for alternatives rather than investing in a cordless system. I'm still working on wearing out the old 18v NiCad cordless tools left over from my construction business.

The corded driver was $23 shipped from fleabay so it was a no brainier to explore if it was feasible to use.

Jay,
You must be my brother from another mother. I had the same idea as what you did. I actually took an electric impact tool apart to see how it can work. Then I sold my Southbend lathe and gave up on the idea.

How is your high speed spindle upgrade coming along?

Rod in San Francisco
 

jbolt

Active User
H-M Supporter-Premium
#13
Jay,
You must be my brother from another mother. I had the same idea as what you did. I actually took an electric impact tool apart to see how it can work. Then I sold my Southbend lathe and gave up on the idea.

How is your high speed spindle upgrade coming along?

Rod in San Francisco
I've been running the spindle for a while now. I like it a lot. It was well worth the time and cost. I'm only running to 6K max which has been enough for me. I'm only running 103 Hz max due to the lesser quality motor and VFD. I could get to 7K with a better motor/VFD. About the smallest cutter I use on that mill is 1/8". I run 1:2 and 2:1 on the pulley ratios which seems to be a good balance. 90% of the time I run on the high belt ratio and can get away with some low speed work. If I'm doing steel I will switch to the low speed. The bellevue washer/pneumatic cylinder drawbar system is not quite strong enough to hold a large end mill for heavy roughing in steel. I get tool pullout if I run too hard in steel. Not a problem in aluminum. I should have gone with a 4-stack cylinder vs the 3-stack. Darn things are expensive.

TomS recently converted his and is running to 9K. I'm not sure how that is working out. I believe he did a 1:2.5 / 2.5:1 pulley ratio. I'm curious how that will work out at the lower end of the high speed range as far as torque goes. May not be a problem with a good motor/VFD. I've stalled mine trying to run below 1K in the high range.
 
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jbolt

Active User
H-M Supporter-Premium
#14
I searched high and low for a definitive answer to this when I was considering using a 220v gear motor. I mostly found the reply to be "torque until it is tight enough". Not helpful.

The torque specs for a 7/16-20 range from about 20 to 90 ft. lbs. depending on the grade of bolt. Somewhere in the middle is probably about right but there are other factors such as dry or lubricated threads etc. that will affect torque. There are a few electric DIY systems out there that are using voltage rise, degree of turn or mechanical stretch of the draw bar as the limiting factor but the electronics to make these work get beyond my knowledge base.

Air impact systems are limited by available or regulated air PSI. For the electric impact driver system it is "torque until it is tight enough". It doesn't take long to get a feel for what is enough just like tightening a drawbar by hand.
 

cut2cut

Active Member
Active Member
#15
Jbolt,

Thank you! A very helpful starting point. I was contemplating using an arduino to control an electric motor. All kinds of possibilities but the method Rod used may be the easiest quiet solution.

Jake