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WTK Power draw bar 4 PM835?
- Thread starter chiroone
- Start date
- Joined
- Jun 27, 2019
- Messages
- 109
I built one. It works over the full quill range but is not the easiest thing in the world to make.
When I switched to a BP "clone" with a quill (and draw bar) that moved a full 5 inches, I wanted the impact wrench to be able to move far enough to tighten or slacken the draw-bar with the quill at any point in its travel. I used two 20mm dia air cylinders with 150mm stroke (from Ebay) to lift the wrench (the same HF one) and a pair of linear shafts and linear bearings to guide it. Adjustable air damper valves on the 5-port valve outlets allow you to dampen the movement so the power draw bar does not slam up and down at full speed. This was not an easy build (the PM mill was not designed to make this easy).
Both of these worked just great and the latter one was really important to me as the mill is very tall, and I am not. I use TTS tooling and a lot of the benefit is lost if you have to climb a ladder to slacken or tighten the draw bar.
If I had a BP then I would probably go with an over-the-counter purchase. I have no idea how the BP keeps the draw bar hex head at the same height despite using a quill. I assume there is some kind of sliding, keyed aspect to the draw bar.
If anyone is thinking of using Bellville washers and some Tormach-type cylinder, or a cylinder and lever construction, then I have six unused Tormach washers available. I gave up on this approach when I calculated the huge forces involved in compressing the Bellville washers enough to slacken the TTS collet. Of course the great advantage of the impact wrench approach is that you can easily use R8 tooling when it is called for. TTS at 3/4" dia does not provide enough grip for serious face milling and quite a few other high torque tasks.
What you can see are the twin pneumatic cylinders (150mm long) needed to handle the full travel of the quill. The picture shows the drawbar at the top of its travel. Normally the cylinders hold up the butterfly ratchet assembly clear of the drawbar. When depressurized by pressing on one of two control panel buttons, the entire assembly quickly lowers on the 20mm linear bearings until the impact socket hits and engages with the hex of the drawbar. This works even if the quill is fully extended as the deep impact socket is small enough to drop through the hole and reach the drawbar. Either push button releases the pneumatic cylinders via a 12v valve and a pair of diodes.
Until this point no air has reached the ratchet as there is a 12v valve controlling it. When the impact socket hits the drawbar, the socket is pushed upwards against the brass ring (you can see the green contact wire in the photo below) and an electrical connection is made between power supply, ring, socket, drawbar and mill body. This turns on the air supply to the ratchet, tightening or loosening the drawbar depending upon which of the two buttons was pressed. Air is diverted by a two-way valve to whichever wrench port is needed to tighten or loosen. Needless to say the brass ring is electrically insulated from the metal that surrounds it.
It did require quite a bit of tuning of air pressures and other adjustments to get it to work, but work it does. I did consider many alternatives including an air pressure sensor rather than the brass ring contact, but this scheme worked best.
I would love to hear of another, more elegant solution to the problem as it isn't the prettiest aspect of the mill, but unless I could grow about 6 inches taller I was faced with a step ladder being a standard part of my milling tool set.
- Joined
- Jun 12, 2014
- Messages
- 5,055
I believe the head on the 835 is similar to the 935, a number of owners have installed the Maxi Torque Rite power drawbar. David Best did a posting on his install below. Best to work directly with the company because you will need a custom drawbar. I use the same system on my knee, works well although I have to set my air pressure a bit higher (100 PSI). Always make sure you spindle is is all the way up and locked when using a power drawbar. Alternative is to use something like an ER-32 system or a quick change system.
www.hobby-machinist.com
www.maxitorqueritedrawbar.com
Power Draw Bar Install on PM TS Style Knee mill
I recently purchased a Power Draw Bar for my PM 949 mill which is a TS style with a cam on top to engage and disengage the direct drive when changing speed ranges. I had talked to Matt at QMT via E-mail awhile back and he sold and recommended purchase of the Maxi Torque-Rite unit which I...
www.hobby-machinist.com
Maxi Torque Rite Air Power Draw Bar: Stock Feeds For Manual + CNC Milling Machines
Call Toll Free @ 800-575-2843 , Maxi Torque Rite Air Power Draw Bar, We sell new + used pneumatic Draw Bar of all styles customized to your needs for milling machines + CNC lathes
- Joined
- Jun 27, 2019
- Messages
- 109
I believe the head on the 835 is similar to the 935, a number of owners have installed the Maxi Torque Rite power drawbar. David Best did a posting on his install below. Best to work directly with the company because you will need a custom drawbar. I use the same system on my knee, works well although I have to set my air pressure a bit higher (100 PSI). Always make sure you spindle is is all the way up and locked when using a power drawbar. Alternative is to use something like an ER-32 system or a quick change system.
Power Draw Bar Install on PM TS Style Knee mill
I recently purchased a Power Draw Bar for my PM 949 mill which is a TS style with a cam on top to engage and disengage the direct drive when changing speed ranges. I had talked to Matt at QMT via E-mail awhile back and he sold and recommended purchase of the Maxi Torque-Rite unit which I...Maxi Torque Rite Air Power Draw Bar: Stock Feeds For Manual + CNC Milling Machines
Call Toll Free @ 800-575-2843 , Maxi Torque Rite Air Power Draw Bar, We sell new + used pneumatic Draw Bar of all styles customized to your needs for milling machines + CNC lathes
Yeah I see the attraction of not building your own but I was unwilling to give up on the ideal of not having to raise the quill to the top of its travel whenever I wanted to change tools. To a certain extent it limits the utility of the TTS approach if you have to keep resetting the cutting height.
I just thought, why should I have to do it when I never had to on my crappy Sieg mill? It was another pretty complex job to make that power draw bar completely automatic.
One other tiny issue is cost. I estimate my system cost about $150 in total, plus quite a bit of time and knuckle skin.
Not sure what a purchased system costs but it looks like it would be about 4 X this much.
- Joined
- Feb 17, 2013
- Messages
- 4,415
I just bought an 835S and noticed that they do offer a power drawbar. A bit spendy for me. I plan to go homebrew with a butterfly impact wrench.. Anyway, here's a link to the one they offer:
www.precisionmatthews.com
Power Drawbar for Step Pulley Knee Mills – Precision Matthews Machinery Co.
www.precisionmatthews.com
- Joined
- Jun 27, 2019
- Messages
- 109
They say PM-935S, PM-935TS, PM-949TS, PM-950S, PM-1054TS with no mention of the 835S (though it probably would work as I'm pretty sure the 835S has a 935S top end) but the build is tricky and took me quite a bit of time. It would have been easy if I accepted that the quill always had to be at the top of its travel to use it.I just bought an 835S and noticed that they do offer a power drawbar. A bit spendy for me. I plan to go homebrew with a butterfly impact wrench.. Anyway, here's a link to the one they offer:
Power Drawbar for Step Pulley Knee Mills – Precision Matthews Machinery Co.
If you want any details of how I made it work at any height, let me know. Also if you find that the special drawbar they must use is available to buy I would be interested in that too.