# Power Drawbar Electric or Air



## Dgrose (Feb 25, 2021)

I just got a Southbend 9x48 milling machine from Grizzly.  They have a power drawbar that is electric.  Most of the ones I have seen are air.  Is one better than the other.  Which way should I go?
Second question:  How does the drawbar stop pulling?  Do you just blip the switch and hope it is tightened?  Can you overtighten the R8 tooling with a power drawbar?


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## Shootymacshootface (Feb 25, 2021)

Don't know about electric, but the air powered drawbar is usually built around a 3/8 impact gun.
And, yes you can over tighten it. You just keep the air pressure at the usually recommended 90psi. It doesn't take long at all to get a sense of how tight to make it.


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## higgite (Feb 25, 2021)

FWIW, Grizzly says their pneumatic power drawbar (PD) puts out 135 ft/lbs with 90 psi air and their 220 volt electric PD puts out 240 ft/lbs. The manual for the pnuematic PD shows a torque adjustment, the electric one does not.

On the other hand, Maxi Torque Rite says their pneumatic PD “can deliver 40 to 50 foot-lbs of torque, not 15 to 25 foot lbs like the competition.”

I have no idea how much torque is not enough, too much or just right. I tighten my drawbar manually “about that much”. Hopefully, someone who knows some real world numbers will chip in.

Tom


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## Winegrower (Feb 25, 2021)

A friend has a pneumatic power drawbar on a vari-speed Bridgeport.   It is actually more of a nuisance than you might think.  There is no way to turn the spindle other than to grab it directly, (as in tramming, for example) and it’s hard to turn if you’re in low gear.  Just putting in an edge finder is more of a project than you might think, there is only one “fits all” torque setting, and if you want to increase or decrease for some operations it can’t be done easily...take off the dome, turn an adjustment, replace dome.  The spindle has to be fully raised or the PD won’t engage.   Maybe if it’s hard to reach the top of the spindle the PD is a must, but otherwise I don’t want one for my mill.


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## projectnut (Feb 25, 2021)

higgite said:


> FWIW, Grizzly says their *pneumatic power drawbar (PD) puts out 135 ft/lbs with 90 psi air and their 220 volt electric PD puts out 240 ft/lbs.* The manual for the pnuematic PD shows a torque adjustment, the electric one does not.
> 
> On the other hand, Maxi Torque Rite says their pneumatic PD “can deliver 40 to 50 foot-lbs of torque, not 15 to 25 foot lbs like the competition.”
> 
> ...


I'm  bit surprised the power drawbars are set for that much torque.  Bridgeport recommends, "Drawbar has 7/16”-20 right hand thread and should be tightened by hand with normal amount of pressure using wrench furnished with machine".

The "normal amount of pressure" for a 7/16'-20 grade 2 bolt is 41 ft. lbs., the normal torque for a grade 5 is 49 ft. lbs.   40 psi to 45 psi is approximately how much torque I apply on my manual drawbar.  Unless you're using a different thread or a hardened drawbar I think you're risking stripping the threads at 240 psi.  You may be stretching them at 135 psi.


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## ttabbal (Feb 25, 2021)

I recently installed a pneumatic on my Bridgeport. It uses the HF butterfly impact, which they claim is max 75 ft/lbs. Translated to real units, that's probably about 40 ft/lbs. Exaggerating air tool torque seems to be an Olympic sport for tool manufacturers.   

There seems to be some debate when I search for R8 torque, but it seems to range around 30 ft/lbs if I average it out. And it sounds about right for what I would normally tighten to. 

I am able to fit the regular wrench in there, so I compared the feel of "tightness" (yeah, real technical).. And it seems to tighten up to about what I would normally do by hand. I've never had a tool slip, so I think it's pretty good. My highly technical method is to let it hit a couple times after it looks to stop spinning freely. Just letting it go indefinitely would likely over tighten it. 

I really like not needing to hammer the collet out. The impact wrench pops it loose easily. The spindle does need to be at the top, but that's the case with a manual wrench as well. 

I usually turn the spindle by using the pulleys when I need to manually clock something in the collet, like tramming tools. Obviously, that doesn't work for vari-speeds.


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## mksj (Feb 25, 2021)

I use the Maxi-Torque air on my knee mill, usually takes about 3-4 seconds to tighten or un-tighten. You can hear when it spins, then locks and I add about 2 seconds to allow full tightening. They are not engaged otherwise. On tramming, with the knee, there is a neutral position where neither hi or low speed range is engaged. When switching between the hi and low range there is two crowns that mesh together when switching to the high range, make sure to check that the gear change lever is fully engaged and hand turn the spindle first to make sure the two crowns are seated together before powering up the spindle.

As far as air vs. electric, might also have to do with if you have an air supply or not. I have seen on bench top mills a number of people using an electric drill for the drawbar, some have a clutch mechanism. The grizzly and a few other electric drawbars are almost twice the price of the air, seems quite expensive.


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## FOMOGO (Feb 25, 2021)

I just use a 3/8 drive air impact, may get around to building the mechanism some day. A short burst on the trigger, maybe 1 sec seems to do the trick, no need to use the spindle brake. Can't ever recall having a tool come loose.  Mike


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## Shootymacshootface (Feb 25, 2021)

I was lucky enough to have a Kurt pneumatic drawbar on my mill. Its very simple and well designed, anyone could build one. I absolutely love having it, but there is one drawback. To use my 90* head, I would have to remove most of it because the quill needs to be lowered 4 or 5 inches to tighten it on. 
Over on PM, Frank Ford has an article about how he modified his 90* head so it can be installed without removing the power drawbar. It is excellent. 
I'm pretty sure that I will be doing something similar to mine at some point.


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## aliva (Feb 25, 2021)

I have a pneumatic draw bar I usually tighten for about 3-5 seconds @ 100 psi. So far so good. 
don't get hung up on torque settings,  just tighten till it doesn't slip. You'll get a feel for it in a short period of time.


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## talvare (Feb 25, 2021)

I have a Kurt power draw bar on my BP mill and after having it, I would never be without one. When seating a collet or tool holder I release the button the instant the tool is seated. Never have had one come loose. Air pressure is set at 90psi. Personally, I think those torque figures for the Grizzly PD are way over rated.
Ted


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## talvare (Feb 26, 2021)

Shootymacshootface said:


> I was lucky enough to have a Kurt pneumatic drawbar on my mill. Its very simple and well designed, anyone could build one. I absolutely love having it, but there is one drawback. To use my 90* head, I would have to remove most of it because the quill needs to be lowered 4 or 5 inches to tighten it on.
> Over on PM, Frank Ford has an article about how he modified his 90* head so it can be installed without removing the power drawbar. It is excellent.
> I'm pretty sure that I will be doing something similar to mine at some point.


I looked at Frank Ford's modification to the 90 deg. attachment and it is a great idea. But, his attachment is an after-market unit which is designed so that the modification is pretty easy to do. Mine is a Bridgeport attachment and I don't see any way to accomplish what he did with his. If there is any information available showing how to EASILY install the Bridgeport horizontal milling attachment on a machine with a power draw bar, I would sure like to see it.
Ted


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## Shootymacshootface (Feb 26, 2021)

talvare said:


> I looked at Frank Ford's modification to the 90 deg. attachment and it is a great idea. But, his attachment is an after-market unit which is designed so that the modification is pretty easy to do. Mine is a Bridgeport attachment and I don't see any way to accomplish what he did with his. If there is any information available showing how to EASILY install the Bridgeport horizontal milling attachment on a machine with a power draw bar, I would sure like to see it.
> Ted


Mine is a Bridgeport head with a nicely contoured casting as well. My son and were just discussing how we could modify ours. I think that the casting is thick enough to attach flanges to the top and bottom halves with a series of machine screws. If we do tackle this project I will be sure to document it here on HM.

Honestly I have never used my 90* head because of the drawbar issue. I have always managed to come up with a work around solution. I would like to change that.


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## Mitch Alsup (Feb 26, 2021)

higgite said:


> FWIW, Grizzly says their pneumatic power drawbar (PD) puts out 135 ft/lbs with 90 psi air and their 220 volt electric PD puts out 240 ft/lbs. The manual for the pnuematic PD shows a torque adjustment, the electric one does not.
> 
> On the other hand, Maxi Torque Rite says their pneumatic PD “can deliver 40 to 50 foot-lbs of torque, not 15 to 25 foot lbs like the competition.”



This might be a good time to point out that the TQ is delivered to the R8 insert by means of the little nose in the slot of the taper and not by pulling tight on the drawbar!

The only thing the draw bar TQ needs to do is to mate the surfaces of the R8 spindle taper to the R8 insert taper.


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## Lttlcheeze (Jul 13, 2021)

mksj said:


> I use the Maxi-Torque air on my knee mill, usually takes about 3-4 seconds to tighten or un-tighten. You can hear when it spins, then locks and I add about 2 seconds to allow full tightening. They are not engaged otherwise. On tramming, with the knee, there is a neutral position where neither hi or low speed range is engaged. When switching between the hi and low range there is two crowns that mesh together when switching to the high range, make sure to check that the gear change lever is fully engaged and hand turn the spindle first to make sure the two crowns are seated together before powering up the spindle.
> 
> As far as air vs. electric, might also have to do with if you have an air supply or not. I have seen on bench top mills a number of people using an electric drill for the drawbar, some have a clutch mechanism. The grizzly and a few other electric drawbars are almost twice the price of the air, seems quite expensive.



I'm shopping around for an electric drawbar, what other ones are there besides the Grizzly one?


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## jwmelvin (Jul 13, 2021)

Mitch Alsup said:


> This might be a good time to point out that the TQ is delivered to the R8 insert by means of the little nose in the slot of the taper and not by pulling tight on the drawbar!



Do you mean the set screw that often goes in the spindle to engage the slot in R8 tooling? Many people remove those. It’s been my understanding that torque is intended to transfer through the taper and not the set screw.


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## Beckerkumm (Jul 13, 2021)

I just put a Maxi Torque on my Sharp VH25.  Cat 40 and head is too high to easily use the manual draw bar.  You quickly develop a feel and you really don't need a lot of torque.  I will probably put one on my big Rambaudi which is 50 taper and it seems like it should handle it.  Maxi torque seems like a good company, helpful, and the only US made one on the market if that matters.  I did find that the draw bar needed about 1/4" taken off to match my machine.

I don't like running the big compressor for the mills so I watch CL and FB mktplace for used Dental compressors.  I have a couple of small Jun air that run silently and put out enough air for my draw bars and the pneumatic blast gates on the woodworking machines.   I like them a lot.  They run forever and cost about $400-500 on the used market.  Dave


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