[jstiltner]

Everyone as seen the pneumatic draw bars using spring washers. I have an idea that I want to expand on, when time allows (junior year in mechanical engineering... dont have time to sleep) Replace the usual lever to press down on the drawbar was an cam that is similar to the one attached here. This was drawn in google sketch up as my inventor is not on this computer. I was planning to turn this with a small dc motor and a set of worm gears This would allow a compact gear reduction that should be self locking. The part will need to be made from steel, or a material harder than steel. Possibly with a bearing material added to the top of the drawbar if wear becomes a real issue.

With a coefficient of friction of .08(static) for steel on steel, and a drawbar force of 1500lb the torque requirement would be .08*1500lb=120lb, in the case of a 1" cam you have 120inlb or 10 ft lb. This is a value for greased steel on steel. There may be issues with deformation of the parts due to the small point of contact.



Questions, Comments, other ideas lets hear em!

Justin

[philbur]

How do you plan to disconnect the motor and worm gear from the cam when the spindle is running.

Phil

I was planning to turn this with a small dc motor and a set of worm gears

Questions, Comments, other ideas lets hear em!

Justin

[SScnc]

I had considered a cam type also but using an arm connected to the cam's center shaft and the other end of the arm connected to some type of linear actuator, pneumatic or other.

I came to the conclusion that to overcome the high friction and wear of direct cam to drawbar either the top of the drawbar would need some type of hardened ball installed or, more practical, a short arm just below the cam which has a roller that makes contact with the cam and the bottom flat of this short bar makes the actual contact with the drawbar and eliminates the majority of the friction and wear. The short bar with the roller would be held against the cam with a spring to clear the drawbar when spinning. Or some type of plunger that moves vertically with a roller on top, like a roller cam follower on a modded engine like one half of

THIS

For me, I decided it was too complicated and found no advantage in going this route but that sure doesn't mean it can't be done in many other forms also and work very well.

Just my thoughts.

[SCzEngrgGroup]

I think a mechanically simpler way of accomplishing the same thing is to use a high-torque rotary actuator driving a screw (ideally a ballscrew), which directly presses on the drawbar. This would give the same mechanical advantage as the cam, but eliminates the troublesome sliding motion. But, you still end up needing a high-torque motor (10 ft-lbs is a LOT of torque!), and for only very slightly more money, you can use a higher-torque motor and directly drive the hext head of a standard non-belleville drawbar. Here's a good source of reasonably priced, high-torque DC gearmotors:

http://www.anaheimautomation.com/pro...or.php?tID=103

Regards,
Ray L.

[BobWarfield]

How do you plan to disconnect the motor and worm gear from the cam when the spindle is running.

Phil

Just arrange the cam shape so that the part with the most clearance (by the "notch" in the drawing) doesn't touch the top of the drawbar.

Best,

BW

[jstiltner]

Bingo bob, that was my plan. While 10 ftlb may sound like a lot of torque, if you look at what the motor(actually a gear motor) will need to output, it becomes more reasonable. if you take a worm gear with 20 teeth that will give you a 20:1 reduction. This will only need to turn 330 degrees or so anyway. The advantage I see here is that you now can put your motor system to the side and perpendicular to the drawbar, IE along the mill head, or at any other angle you wish really. I hope for less than 1 second release / engage time. Although, if you dont care about your collets / taper / etc., the engage time could be almost instant...

[philbur]

I assume the proposed design was attempting to get rid of the spring washers, maybe I misunderstood.

Phil

Just arrange the cam shape so that the part with the most clearance (by the "notch" in the drawing) doesn't touch the top of the drawbar.

Best,

BW

[jstiltner]

Nope, still having the spring washers there, This will only replace the piston and lever that is used to press ontop of the drawbar to compress them.


I am planning to use a motor from bane bots, ive used them before, and while not super quality, for the price they cannot be beat on the new market.

Specifically one like this
http://banebots.com/c/MP-36XXX-385 I would use the smaller size, but I dislike metric system for machine parts.

[philbur]

Have you run the numbers. does such a motor have the umph to do the job in a reasonable time period.

Phil

Nope, still having the spring washers there, This will only replace the piston and lever that is used to press ontop of the drawbar to compress them.


I am planning to use a motor from bane bots, ive used them before, and while not super quality, for the price they cannot be beat on the new market.

Specifically one like this
http://banebots.com/c/MP-36XXX-385 I would use the smaller size, but I dislike metric system for machine parts.