I have 2 known R8 tools that for some reason were tapped about 0.1-0.2" shallow. So the draw bar bottoms out on the tool thread before the R8 taper is seated to the quill taper. I'm thinking of making a 0.2" thick steel spacer collar that resides under the hex portion which effectively raises the rod. I would have it retained with a lateral set screw so that when I remove the drawbar, the spacer comes with it. Anybody see any adverse issues with this idea?
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935-TV - spacer under drawbar
- Thread starter petertha
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Peter, I’ve done the same thing only I used an O-ring tight fit to the drawbar OD to retain the washer rather than a set screw.
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Your idea should work just fine, well thought out.
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I made a spacer for one of my tool holders, and I didn’t use any retention device. Sometimes it comes out with the drawbar, sometime it doesn't. It's easy to fish out with my fingers if it doesn't. Seems to me like one more step you may not need.
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Had the same issue on my knee mill and almost sheared off the guide pin in the spindle. The arbor was partially damaged. In my case I have a power drawbar and the height of the top of the drawbar has to be set to a very specific height. There is a collar on the top of the drawbar that must sit just slightly below the mounting plate for the power drawbar unit. In either case, I opted to check all my R8 tooling and I only had one arbor which the threads/hole was not deep enough for the drawbar. It got tossed along with the guide pin, and I am more careful if I buy any new R8 arbors. With a manual drawbar I do not see that that a spacer would be an issue, and it is an easy alternative. If I had an issue with multiple arbors I would have ground down the threaded end of the drawbar in increments. Never had an issue with my last mill with the same arbors, so very good reminder for others. Always learning something new....
I like Davids idea more than mine. Less fiddly to make & no way for a small part like a set screw to loosen & get sucked down into the turbine LOL.
I chose an appropriate O-ring from my 5$ super deluxe AliExpress graduated kit. I think it happened to be 14mm OD x 2.5 mm section. Whatever is snug-ish fit on the draw bar shank. Turn the steel spacer disc to match OD of drawbar, drill ID to clear the rod, counterbore recess the end so the O-ring fits inside. Voila. I made mine 0.275" thick but your mileage may vary. Now I can use my favorite Jacobs chuck again.
I can visualize the potential problem Mark was mentioning about the spindle guide pin interfering with the shallow threaded R8 shank under drawbar power. That would be a bugger. It almost happened to me just tightening with a socket wrench before I noticed what was going on. Fortunately a few tap-taps on the drawbar & it came out again. So I guess the moral is to be aware with any new arbor tool acquisition. Tighten it gently, ideally by hand the first time to ensure it seats properly. Measuring the thread depth alone is not that meaningful because it could be the shank itself is a slightly incorrect length. While you are at it, check the thread condition or run a tap into it. The odd time I've found mung or worse yet machining shrapnel in one of my end mill holders. So sense buggering up the drawbar threads.
I chose an appropriate O-ring from my 5$ super deluxe AliExpress graduated kit. I think it happened to be 14mm OD x 2.5 mm section. Whatever is snug-ish fit on the draw bar shank. Turn the steel spacer disc to match OD of drawbar, drill ID to clear the rod, counterbore recess the end so the O-ring fits inside. Voila. I made mine 0.275" thick but your mileage may vary. Now I can use my favorite Jacobs chuck again.
I can visualize the potential problem Mark was mentioning about the spindle guide pin interfering with the shallow threaded R8 shank under drawbar power. That would be a bugger. It almost happened to me just tightening with a socket wrench before I noticed what was going on. Fortunately a few tap-taps on the drawbar & it came out again. So I guess the moral is to be aware with any new arbor tool acquisition. Tighten it gently, ideally by hand the first time to ensure it seats properly. Measuring the thread depth alone is not that meaningful because it could be the shank itself is a slightly incorrect length. While you are at it, check the thread condition or run a tap into it. The odd time I've found mung or worse yet machining shrapnel in one of my end mill holders. So sense buggering up the drawbar threads.
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I have a newer PM-935TS and noticed that the drawbar had no washer on it, but the manual shows one. I asked PM about this and they said they havent ever come with one. While I haven't yet had a problem bottoming out the drawbar in the collet threads, I have noticed that it threads much further into collets than any other mill I've used. I also didnt want the drawbar marring the top of the spindle so figured a hardened washer was the best approach.
Since the washers are supposed to be hardened, I opted for just buying one. I spoke with Kurt to figure out what the dimensions were on all their washers and found that the 603-06 Drawbar Washer, and the 605-02 Drawbar O-Ring (Buna N, #014) were the right fit.
Hope this helps someone else out.
Since the washers are supposed to be hardened, I opted for just buying one. I spoke with Kurt to figure out what the dimensions were on all their washers and found that the 603-06 Drawbar Washer, and the 605-02 Drawbar O-Ring (Buna N, #014) were the right fit.
Hope this helps someone else out.
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I like this idea....41 years ago as a new design engineer at Ford transmission and chassis division, we needed an inexpensive way of holding the speedo gear onto the retainer bearing. Without something to hold the speedo gear in position it would fall into the transmission with no easy way to get it back out. The first design was with a roll pin to hold the gear on. Problem was the retainer bearing had to have a hole drilled in it which added an operation never mind the cost of the roll pin. I suggested that an o-ring be used. We were able to make an easy change to add a grove on the speedo gear stem.
Orings work great in these situations.