Any clever ideas to fix this problem?
Any clever ideas to fix this problem?
(OP)
Hi all,
I have a cylindrical mandrel (0.34" OD) that has a 0.188" flat to flat hex recess broached into one end of the mandrel. A hexagonal bit fits into this 1" broached recess, and the bit has an oversized ring on the end that expands into an undercut once it is inserted far enough into the mandrel. This is to ensure that the bit cannot be pulled out of the mandrel while it is in use. To remove the bit, we have a hook tool that fits into a pilot hole on the mandrel and acts as a cantilever on the back of the bit that allows the snap ring to compress and the bit is ejected. The problem is, we are lengthening the bit and the recess, and once the snap ring is cleared of the undercut by the ejection tool, it is still too hard to remove by hand. I have been asked to redesign the mandrel so that the bit cannot be pulled out during service, but then can be easily removed when needed. At first i thought of a ball detent, but the assembly required is outside the budget for this part. I'm just looking for a clever mechanism that can achieve the same function that I described. Any suggestions would be greatly appreciated.
Thanks,
M
I have a cylindrical mandrel (0.34" OD) that has a 0.188" flat to flat hex recess broached into one end of the mandrel. A hexagonal bit fits into this 1" broached recess, and the bit has an oversized ring on the end that expands into an undercut once it is inserted far enough into the mandrel. This is to ensure that the bit cannot be pulled out of the mandrel while it is in use. To remove the bit, we have a hook tool that fits into a pilot hole on the mandrel and acts as a cantilever on the back of the bit that allows the snap ring to compress and the bit is ejected. The problem is, we are lengthening the bit and the recess, and once the snap ring is cleared of the undercut by the ejection tool, it is still too hard to remove by hand. I have been asked to redesign the mandrel so that the bit cannot be pulled out during service, but then can be easily removed when needed. At first i thought of a ball detent, but the assembly required is outside the budget for this part. I'm just looking for a clever mechanism that can achieve the same function that I described. Any suggestions would be greatly appreciated.
Thanks,
M





RE: Any clever ideas to fix this problem?
Ted
RE: Any clever ideas to fix this problem?
We also used light duty spring pins that you could push out by hand with a pin punch. We also used spring wire retainers that would expand into a groove in the chuck. You would grab the bit with a vise-grip to pull them out.
It doesn't take a lot of force to retain a bit so you don't have to be very heavy duty.
RE: Any clever ideas to fix this problem?
RE: Any clever ideas to fix this problem?
RE: Any clever ideas to fix this problem?
RE: Any clever ideas to fix this problem?
RE: Any clever ideas to fix this problem?
RE: Any clever ideas to fix this problem?
RE: Any clever ideas to fix this problem?
http://www.carrlane.com/catalog/index.cfm/27025071...
Ted
RE: Any clever ideas to fix this problem?
RE: Any clever ideas to fix this problem?
I purchased a knife recently that uses I think a very ingenious locking method.
a small straight spring when the blade is pulled open it locks in place.
to unlock it push on the spring to disconnect it. marveles.
if it would be possible have a small spring in the mandrel that locks the bit
when it is inserted to the mandrel.
Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.
RE: Any clever ideas to fix this problem?
If I am understading correctly would something like a ball lock not work?
RE: Any clever ideas to fix this problem?
Ted
RE: Any clever ideas to fix this problem?
RE: Any clever ideas to fix this problem?
Morse taper size 0 ?
Ted
RE: Any clever ideas to fix this problem?
Basically the centre line for the spherical balls is such that an exact integral number will lie on the groove. The midpoint of the groove lies at the interface of the drill bit to mandrel bore. Was hoping you had a picture, I could be much more exact.
Analysis of fracture mechanics, resistance force is a function of shear through the diameter of balls times the population housed in the groove common to the Mandrel and Bit. The joint takes a considerable amount of bit bounce and drill string vibration, so it is fairly robust for your application.
Good luck with it.
Regards,
Cockroach
RE: Any clever ideas to fix this problem?
RE: Any clever ideas to fix this problem?
RE: Any clever ideas to fix this problem?
RE: Any clever ideas to fix this problem?
RE: Any clever ideas to fix this problem?
Clear as mud right.
RE: Any clever ideas to fix this problem?
i like this idea
Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.
RE: Any clever ideas to fix this problem?
http://www.mcmaster.com/#retaining-rings/=jzn0sj
Ted
RE: Any clever ideas to fix this problem?
I think the challenge would be to get chip flow out of the broached hole of the female piece. Most likely you would machine this recess after broaching, I think a long continuous path for the shaper would be best in terms of an interrupted cut.
I also prefer liquid nitration as a case hardening process in order to reduce the metal-to-metal transfer between mating components. It also removes the free iron from the surface of the pieces, hence no rusting.
I've used similar ideas like this in the past, works okay, nothing special though.
Regards,
Cockroach
RE: Any clever ideas to fix this problem?
This seems like a perfect idea, and should work for my application. The bit pullout needs to withstand 70 lbs, do you think this is possible? Also, can you explain your design in more detail, I'm still a little confused on how the locking mechanism works. Thanks so much for the help, you're a life saver!
-M
RE: Any clever ideas to fix this problem?
To release, I have three 1/16 holes circumferentially around the female. Simply insert an o-ring pick or equivalent into the holes to push the Lock Segments down. Pulling back on the male shaft will disengage the components and allow for dis-assembly. Spring force is light, no much is required.
A guy could do the same with a telescopic pin, spring activated, running orthogonal to the male hex shaft. In this case, the pin would snap into a hole or groove in the female, so close to what we have here. That would have a big cost advantage compared to what I did, but the prints you have take much more load, 70 lbf is relatively easy to obtain. But as mentioned, I would do the stress mechanics on the system in order to validate the design for your input statements and requirements.
There are other examples as well, this is not a particularly challenging design problem.
Good luck with it. Chip flow from the internal bore of the female while cutting the recess, I think that would be the issue. Hopefully it is a bore thru design, I've shown it closed ended only to mirror what your initial requirements where.
Regards,
Cockroach
RE: Any clever ideas to fix this problem?
The female part will take 5,011 lbf, the wall of the recess being the weak point. Note that it sees no torque because I extend the hex above and below that recess, loading IS NOT thru the wall of the recess. I should of seen that for the male, but following the above would eliminate the limitations in torque.
So I think this would meet your requirements once you make the above noted quick fix.
Regards,
Cockroach