# All Electric Power Drawbar



## jbolt (Feb 14, 2017)

I'm not sure this is the right forum for this but it is electrical so...

I recently acquired a heavy duty drill press with a R8 spindle. I have gotten spoiled with the pneumatic draw bar on my CNC mill and the TTS tooling system.

I would rather not do any type of pneumatic system on this machine so I was thinking about an electric system. I see Griz has one for BP type machines but at $1100 that's out of the question. If I can't diy it for 1/3 that then I'll look at pneumatic.

The Griz unit looks like it uses a 22ov gear motor but give no specifications other than 2100 rpm, 7.5A  and 240 ft/lbs of torque. How would one go about finding a similar gear motor? I poked around a bit but most I found listed torque in in/lbs and no where near what Griz is claiming. 

The other question is how much torque do you really need?


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## intjonmiller (Feb 14, 2017)

Commenting mostly to follow as the subject intrigues me, but wouldn't a relatively low power cordless impact driver and a simple mount for it be sufficient? I am fully aware that I am asking out of ignorance, so no need to say it quite that way if I'm way off base.


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## jbolt (Feb 14, 2017)

intjonmiller said:


> Commenting mostly to follow as the subject intrigues me, but wouldn't a relatively low power cordless impact driver and a simple mount for it be sufficient? I am fully aware that I am asking out of ignorance, so no need to say it quite that way if I'm way off base.



I have seen corded electric impact systems and I originally had a pneumatic impact system on my mill but I generally dislike the pounding on the draw bar and spindle. I would prefer a less abusive solution but it may come to that.


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## intjonmiller (Feb 14, 2017)

Torque-limited electric drill? I wouldn't expect the low or even medium torque setting on a variable torque impact driver to do any damage (they strip fewer fasteners by applying rapid, brief moments of torque or "hammering" rather than sustained torque), but again I'm not certain.


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## talvare (Feb 17, 2017)

I'm pretty sure if you use a driver system without the "hammer" feature, it will require a significantly larger and more powerful motor to break loose (unscrew) the drawbar. You could experience the differences by doing a task such as taking off the lug nuts on one of your car's wheels using a driver without the hammer feature and then use one with the feature.  The increased torque required without the hammer feature will likely induce a lot more stress to what ever mounting structure you construct as well. Just some food for thought.

Ted


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## FOMOGO (Feb 17, 2017)

I use a 3/8" air ratchet by hand, as I haven't gotten around to building anything more sophisticated yet. Just by feel, I'm thinking a clutched drill /driver would probably be more than sufficient on my BP.  Haven't noticed any damage to the draw bar using the air ratchet (easy does it), which can be easily modulated also.  Probably six of one, half a dozen of the other, but both are faster than the brake and a wrench. Mike


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## mksj (Feb 18, 2017)

The Griz specs are peak amperage and maybe locked rotor or momentary peak torque. At that level it would break the drawbar if that was continuous and the motor would be huge. I would look at an electric impact drill or something with a clutch so you could set the torque limit. Might look at the attached PDF file. If you already have air, then you could get/make an inexpensive air unit.


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## brino (Feb 18, 2017)

I'd think a system could be built around a low cost linear actuator.
https://en.wikipedia.org/wiki/Linear_actuator

Searching "linear actuator" brings up many possibilities. Like this one:
http://www.ebay.com/itm/Heavy-Duty-...566020?hash=item3a986fc944:g:hfYAAOSw7NNULaHj

I actually got something similar out of a treadmill I dissected for the main motor. 
It was used to tilt the entire unit by lifting the front end off the floor a few inches for inclined walking/running.

This places has many choices and various price points:
http://www.surpluscenter.com/electrical/linear-actuators/dc-linear-actuators/

-brino


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## rwm (Feb 18, 2017)

I don't know that the linear actuators would have enough force to hold it. 
If your motor provides the same torque in forward and reverse, you could end up with not having enough torque to break the draw bar loose. Ideally you would have a smooth driver to tighten and an impact driver to loosen (or at least greater torque.) Could an impact driver be rigged this way? i.e defeat the impact function in forward but not in reverse?
R


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## brino (Feb 18, 2017)

rwm said:


> I don't know that the linear actuators would have enough force to hold it.
> If your motor provides the same torque in forward and reverse, you could end up with not having enough torque to break the draw bar loose.



Thanks! Interesting questions.
I do not have an answer. I have not made one, just speculating what may be possible.
But you raise a great point. I should preface those ideas with a warning.

Warning: If anyone does build one it is up to them to ensure that the gripping power is enough to hold the tools during use!

-brino


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## Ben Nevis (Feb 19, 2017)

I used a cordless impact driver on my RF30 mill with good success before I switched to a Bellville washer drawbar with TTS system.

http://www.hobby-machinist.com/threads/power-drawbar-for-rf-30.42278/


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## jbolt (Feb 21, 2017)

Thanks everyone for the replies. 

After much digging and researching, while my gear motor idea is doable, the electronics necessary to make it work get out of my comfort zone and the effort required is not worth the time and $$$ for this particular machine. 

I was able to locally see a system using the guts from a 1/4" cordless impact driver that works very well with plenty of torque for an R8 collet. Actually faster and no where near as obnoxious as the air impact system I originally had on my other mill. 

I would rather not deal with batteries for a cordless system so I found a 110vac corded impact driver. If I find it has the required torque then I will modify it for a permanent setup.


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