this message is pretty much directed towards bob, but also anyone wha can help. I wanted to know if anyone has removed the pin inside the r8 spindle. From the conversation on the iso30 spindle it seems that the pin can be removed without any ill effects. Is this true? I have the same power drawbar from joe that bob has, and put the extra clips and springs on it like bob's. I would like to know as this would expidite my prototype attempt at an atc.
Aaron has said somewhere you can pull the pin. That's good enough for me.
Apparently it is accessible if you extend the quill fully through a slot. That makes it easy to test. Pull the pin, insert your biggest nastiest cutter, set the deepest depth of cut you commonly would use, and see how it works before/after pin. Let us know.
Best,
BW
Whether the tool will slip in the taper is primarily a function of how hard you pull on the draw bar versus how much torque you wish to transmit. The answer is almost for sure calculateable, at least to put you in the ball park, add 50% safety margin and you would be home and dry. Its looks like a relatively straight forward coefficient of friction calc.
Regards
Phil
Originally Posted by krymis
this is exactly what i needed to hear. now i just need to set everthing up to get this done. At the moment i have my mill torn apart back to bare bones trying to tidy my conversion back up.
bob,
what size support rods did you use for your PDR? I used .500 for mine and my springs were not as big or long as the ones you used. Do you think this will last? I am kinda concerned about that part....Where did you get your springs too?
Here is a typical calculation. What is intersting is that if you half the speed but still want to transmit full HP then the draw bar tension needs to double. So overall it looks OK for 2 hp as long as you have a draw bar tension of around 1000 lbs and don't go below 200 rpm.
Cone Clutch Calculation for a R8 Taper from (Machinerys Handbook)
large radius of R8 taper r1 1.25 inches
small radius of R8 taper r2 1 inches
half R8 taper included angle a 8.425 degrees
coefficient of friction f 0.7
horse power H.P. 2 hp
spindle speed N 200 rpm
safety factor S 1.5
mean R8 taper radius r 1.125 inches
min. draw bar force Ps 1007.2 lbs
Regards
Phil
Yeah, they are about 1/2". BTW, Vince on these boards (N4NV or some such name) has a Bridgeport he converted and he just built the same drawbar. Looks like he got his to work without return springs, so he musta had a stronger cylinder spring. He's got a post over on the Bridgeport section with a nice movie. Like me, he couldn't resist cycling a tool in and out when he first got the thing working. I was using mine this weekend and it was heaven. Anyone reading this needs to get a set of plans if you don't already have this gadget!
I bought my springs at Ace Hardware. Just grabbed the first thing that looked close. You have to adjust the tension by moving the collars up or down so the is enough force, but not so much the cylinder has trouble engaging smoothly. Frankly, I would have been happier to get mine to go without the springs. I keep pondering a mod to have those rods slide in some UHMW plastic bushings for better performance, but haven't done anything on it.
Krymis, I don't know why yours wouldn't last pretty well. These are not actually high duty devices. Even if you go CNC an ATC, I can't imagine you'd wear it out that fast. Might consider an inline oiler for your impact wrench if you plan to work it hard, though.
FWIW, I have a 3" diameter 7-insert Lovejoy facemill (expensive, but I got a great FleaBay deal and love the cutter) that is my heaviest cutter. Incidentally, it cuts well on the IH mill and leaves as nice a finish as my flycutter did but with much less noise and much faster. I suspect I can do even better if I get some coolant and really dial in optimal feeds and speeds. Anyway, it is good to know the mill is rigid enough to run this cutter on steel, but if I decide to pull my pin, I think this would make a good test.
Philbur, good calculation. We'll want to consider whether there might be a little oil that affects the Cf. I know my stuff has a little Break-Free on it to fight rust--live near the ocean. Certainly explains why the retention knob world uses such a big stack of Belleville washers to hold onto their toolholders. FWIW, there is a company making an R8 change system that claims 600lbs of springing is sufficient on R8. That's close enough to you number of 1000 to make sense. They just thread retention knobs into R8 collets and mill holders. Interesting approach. Don't know that I would prefer it over the power threaded drawbar though. Their system sure is expensive.
Best,
BW
From my experience, drilling (especially large diameter drills) will be the real test.
thanks guys good to know where everything stands.
anymore info on this subject would be great.
I think this is an interesting point.
Providing you are driving the drill into the work-piece the resistance to slipping in the spindle taper is self-compensating due to the increased force pushing the tapers together. However if you slack off for even a fraction of a second (as in pecking, or just to allow the chips to clear for example) then the tendency will be for the partially formed chip to pull the drill out of the spindle. This will have a tendency to relieve the force holding the tapers together and possibly allow the tool-holder to rotate in the spindle. A clear example of this is the problem with large tapered shank drills in the tail-stock of a lathe.
If you use spring washers with an air actuator and stud arrangement for tool release then your retaining force is limited to the spring washer force which is constrained by your desire not to damage you spindle bearings during activation (unless you are very clever with the design). If you use an air wrench solution then the draw bar tension is only limited by the strength of the draw-bar and the power of the wrench.
So if you really want to make a R8 ATC (a dubious proposition at best) without a drive key then the air wrench solution would appear to be the better solution. If you just want quick-change capability then leaving the drive key in place would probalby be a safer option, either with the spring washer or the air wrench arrangement. Personally I don't think that lining up the keyway is that bigger deal for a manual quick-change solution. Alternatively a damaged spindle taper could reduce you to tears, and I hate to see a grown man cry.
Regards
Phil
Another interesting modification to the air wrench design might be to include a thrust ball bearing between the underside of the drawbar nut and the top of the spindle. A 51101 looks suitable - 15mm ID and 28 mm OD - max static load 3000 lbs. This would ensure that more of the applied torgue finds its way down to the tool holder.
Regards
Phil
Interesting thing about drills if they are the worst case:
There's no drive pin in the Taper to Chuck interface. Sure looks like similar or less surface area too.
In the end, it is easy to just try it out on the IH rather than spend hours wondering.
Best,
BW
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