Pneumatic power draw bar on PM932M-PDF

For anyone interested.
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I used Compression spring C-742. Wire diameter: 0.054". Outside diameter: 0.625". Overall length: 2.75".
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It is a common spring stocked by most car part stores.
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Since I used drill rods which are ½” to the thousands of the inch the springs
are absolutely perfect.
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Here are couple of websites.
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http://www.bmr.co/en/anchors/nuts/springs/031215-compression-spring-c-742.html
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http://www.shaffers.doitbest.com/Door+springs-Century+Spring+Corp-model-C-742-doitbest-sku-749417.dib
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http://www.ebay.ca/itm/Century-Spring-C-742-Compression-Spring-Open-Stock-for-display-for-300-2-L-/131080496332
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Regards to all,
Radek
 
What kind of torque is the impact putting out? Actually what kind torque should be on the draw bar.
 
What kind of torque is the impact putting out? Actually what kind torque should be on the draw bar.


I'm not saying this is right but I just started using a little butterfly impact for this, my impact has settings up to 8 and after some experimenting and repeated testing using my torque wrench for reference/calibration a setting of 7 on the impact running at 100psi gives me the exact (or near enough) tension I was applying with the wrenches, 180 inch lbs.
At the moment though I have the worlds most pathetic mount until I have more time, the impact is hanging on a bungeecord by the head of the mill.
 
What kind of torque is the impact putting out? Actually what kind torque should be on the draw bar.

I would like to shine some light on this subject, however how tight the drawbar should be is a somewhat controversial issue.
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Not enough torque could cause little guide to break and spin the R8 tooling in the spindle. Too much torque will make the R8 tooling hard to remove.

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Please bear in mind that R8 Tooling is not as sensitive as Morse taper due to it’s steeper angle.
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In my case the tool is capable of producing a torque of 75Ft/lbs which is way too much for 7/16 – 20 draw bar. My air pressure regulator for this system is presently set at 75 to 80 PSI and I do not use the setting on the tool itself. If I hit the trigger of the butterfly impact tool for the draw bar just to become snug and then hold it for half a second I end up with 10 to 15Ft/Lbs torque which seems to work for me in most light milling applications. For heavier cuts I hold the trigger for two seconds and result is about 20Ft/Lbs torque. So far I did not run into any ill scenario.
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I would imagine there is some variation in different tools and one’s feel to work with pneumatic tools, so I would suggest you lock the spindle and turn down the air pressure and give the tool little spin. With spindle locked put the torque wrench on the draw bar with say 5 ft/lbs setting and start turning and as soon as you see the draw bar turn, stop and read the torque wrench. Keep increasing time and air pressure till you satisfied with correct torque.
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Now what is correct? Tormach has a very nice article about this issue and talks about no need to exceed 30Ft/lbs.
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Here is a link to the publishing. If you have trouble downloading it, let me know.
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http://www.google.ca/url?url=http://www.tormach.com/uploads/163/TD31090_ToolHolding-pdf.html&rct=j&frm=1&q=&esrc=s&sa=U&ei=_DDAU63dHIeIjAKS5oGYAQ&ved=0CFYQFjAO&usg=AFQjCNG_tS9NEXJH_WX-HaQLHSKzrNPZBw
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Hope this helps.
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Radek
 
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In my case the tool is capable of producing a torque of 75Ft/lbs which is way too much for 7/16 – 20 draw bar.
Radek

Did you get your impact at Princess auto? It looks the same as mine and after the testing I did, though admittedly crude, I'm fairly curtain I'd not get 75 ft pounds, but then I'm using a very little compressor with a small tank, it cycles every time I change a tool, where the hell did you get a 12 point socket I look all over and was only able to find 6....?

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Did you get your impact at Princess auto? It looks the same as mine and after the testing I did, though admittedly crude, I'm fairly curtain I'd not get 75 ft pounds, but then I'm using a very little compressor with a small tank, it cycles every time I change a tool, where the hell did you get a 12 point socket I look all over and was only able to find 6....?


Yes, the little impact gun was purchased at Princess Auto. I purchased two of them when they had them on sale $29CND regular $39 something. They had another model on sale (which looks the same) for $18. I was going to purchase third one to lower my average cost, but it turned out it was of much lesser quality (not that this one is anything special). Since I like tools I was going to purchase Chicago Pneumatic, but for what this thing is doing, I can purchase five cheap ones. The model I have is 8344137.
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You are correct, it is unlikely it will produce 75Ft/lbs. I should likely correct my statement. I guess it was more of a warning to anyone so they do not over tighten the draw bar at first go. The box indicates max torque 75Ft/lbs. I definitely would not tighten the wheels on my car, with this little thing, which calls for same torque.
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Found a 12 point socket in my toolbox, it was Craftsman to boot. Used to throw 12 point socket out as they would slip on rusty nuts. FYI, I purchased new draw bar from Enco and it has a ¾” Hex. I looked in my toolbox to see if I got any other ¾” 12 point socket and then it dawned on me you may have the original bar which takes 17mm socket did not find any of them either. Found 11/16” 12 point Craftsmen which is 0.5mm larger then 17mm which may work. If you want, I’ll throw it in the mail, no charge.
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For those curious</SPAN> about name Princess Auto (who the hell shops for man cave tools at Princess?)</SPAN>
The first store opened way back on <st1:Street w:st="on"><st1:address w:st="on">Princess Street</st1:address></st1:Street> in <ST1:p<st1:City w:st="on">Winnipeg,</st1:City> province of <st1:State w:st="on">Manitoba</st1:State>.


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Thanks for the reply Ratz, I have the same impact, I suspect the torque is low for me using a small compressor, no volume in the tank, I was surprised when looking for sockets I remember years ago it was hard to find a 6 point, LOL, now it seem reversed, I'll need to keep a lookout at yard sales and grab a couple of 3/4 sockets.
I needed to make a new drawbar the original had a square end, the impact is great though since replacing the spindle motor in the CNC I now needed 2 wrenches for a tool change because I needed to remove the spindle lock to accommodate the new spindle motor.
When I get more time I'll do something similar to what you did, I'll not be able to
orientate the impact the way you did the new motor is in the way, I'll need to rotate it 90 degrees, but even for now its much better than 2 wrenches for a tool change.
Thanks for taking the time to post your setup, it was kind of you to share.
:))
 
That's an elegantly simple design. I like it so much that I bought the impact today from harbor freight and am starting to gather materials to make my own.

Can you elaborate on the bushings you used and how the handle setup is designed?

Thanks for you posting this. It's great help to me.
 
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