Any clever ideas to fix this problem? 2

[metalman8357]

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

 

[MintJulep]

 

[LewisWHilliard]

Basically you would just slot the mandrel to align with the current circlip location to commiserate with bit engagement. Then make a U shaped spring steel clip slightly wider than the slot. With the clip in place you will have pinned the bit on two side using existing locking features. Removal of the clip is performed with a flat blade screwdriver by tapering the lower edge of the slot to allow acces to the clip.

Clear as mud right.

 

[mfgenggear]

B

basically you would just slot the mandrel to align with the current circlip location to commiserate with bit engagement. Then make a U shaped spring steel clip slightly wider than the slot. With the clip in place you will have pinned the bit on two side using existing locking features. Removal of the clip is performed with a flat blade screwdriver by tapering the lower edge of the slot to allow acces to the clip.

Clear as mud right.

i like this idea

Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[hydtools]

Perhaps an e-ring adapted.

http://www.mcmaster.com/#retaining-rings/=jzn0sj

Ted

 

[Cockroach]

There are a few things you can do, along the lines of the attachement. A guy could come up with similar mechanisms based on this model, I had a telescopic pin concept rather than the Locking Segments, but not sure of your loads. You mentioned robustness, this would definitely meet that criteria.

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

 

[metalman8357]

Cockroach,

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

 

[Cockroach]

Basically, you have a hex nut (Locking Segment) that is activated by a Compression Spring. The male is inserted into the female and by hand, those segments are compressed flush to the male shaft. This allows passage into the female, aligned with the internal hex. Continuing to push the male to the female, they shoulder out at which time the Lock Segments encounter the recess and "snap" outwards due to the Spring force below. The system is now locked into place longitudinally (axially) with the hex shaft taking the torque.

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

 

[Cockroach]

Just a quick and dirty, the male part will take 2,556 lbf of axial load, but is subject to failure in shear due to torque at 5.284 ft lbf. That's because the relief machined in for the hex is only 0.172 inches in diameter. The quick fix here would be to counter bore the opening of the female and push the hex of the male past that opening to the right. You could then remove the counter bore and simply mill the hex to the male shaft and have a flank angle run-out at 30 degrees to the OD of that shaft. Simple.

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