A Crank Handle is more difficult than I thought

[randyjaco]

OK I thought this was going to be an easy project. As you can see the knee crank handle to my Bridgeport clone is missing a few teeth and it is about time I did something about it. So I bolted up my rotary table and started at it on a test piece of aluminum. What the ___, this doesn’t work???

The seven teeth are segments of an annulus kinda trapezoidal in shape. The bottom width is .350” the top width is .250” and the height is .235”. See photo. The OD of the cylinder is 1.578”.
When I put this on the rotary table, I end up with rectangular teeth. There has got to be some relatively simple way to make this part on a manual mill and a rotary table, but I sure can’t figure it out.

Any suggestions would be appreciated.

TIA

Randy

http://i640.photobucket.com/albums/uu124/randyjaco/P1010002.jpg

http://i640.photobucket.com/albums/uu124/randyjaco/P1010001.jpg

http://i640.photobucket.com/albums/uu124/randyjaco/P1010003.jpg

[uute]

Can you "form grind" an endmill like a shallow angle dovetail cutter?

Otherwise, tilt rot. table & use small EM to angle teeth. a small under-cut at bottom won't hurt.

CT2
edit: or if you just want to get it done - hog w/ EM, then File or Dremel!

[pcarpenter]

I hope Frank Ford will forgive me for being the one to post the link to his explanation on how to do this. Frank's site is nicely done and he is a very practical guy with lots of tips on the way he has done things...including making a lot of handy tooling items. A knee handwheel was one of them. I remembered reading about this and the fact that the job was actually much easier than it would seem:

Edit-- I think the part that creates the trapezoidal teeth is the fact that the cut is made with the 3/16" end mill with the *edge* of the cutter on the center of the part...rather than the center of the cutter on center.

http://www.frets.com/HomeShopTech/To...handwheel.html

Paul

[Frank Ford]

I cut the hub of an eight-inch handwheel for my mill knee:



It works MUCH faster than the crank, and because I don't do heavy work, I've not used the crank in about five years.

At first blush, the nine tooth fitting seemed a bit daunting, but as I stared at it for a while, I realized how easy it would be to machine. I didn't think to take pictures of the job, so the best I can do is a quick description. The key to the operation became apparent when I noticed that the upper and lower edges of opposing teeth were in a direct line that exactly bisected the diameter of the shaft:



So, all I had to do was center the hand wheel on my rotary table, and cut a straight slot with a 3/16" end mill across both sides of the hub, making sure the edge of my cut was at the center of the hole. Once I'd made nine passes (turning the rotary table 40 degrees for each) I had the job done - and it was a light press fit into the teeth on the knee screw. I haven't even bothered with a set screw, so I can slip the hand wheel off easily and stick on the crank.

EDIT: Paul, thanks for the mention - you got in there just as I was putting my post together.

[Jim Shaper]

It's not that hard.




Mine's an excello, so the BP ones won't fit (those goofy Canadian's eh!). My mill didn't come with anything for the knee, so I got to make both the wheel I've gone to now, and the original crank handle I used to use.

[oldtiffie]

Cogged

Randy,

Frank Ford's method applies to most of these - irrespective on number of teeth.

When these were originally made they were cut on a horizontal mill with a side and face cutter, so they did a face of two teeth at at the same times and had adequate "run in" and "run out" space for the cutter.

Horizontal mills and cutters work much better than end milling cutters in these situations.

I was about to reply pretty much the same way as Frank but got "called away".

The answer was pretty obvious from putting the edge of a sheet of paper over the teeth in your second pic.

Set the edge of the cutter in line with the centre of the job, make the first pass/cut on all "teeth", then re-set for the second face - but "ease" into it.

Its only a simple multi-toothed dog clutch after all.

It (usually) only works this way with odd numbers of teeth.

[Ken_Shea]

Randy, when you're done and I am sure you will get it, and if you are still using the original long handle, be sure and drill the center shaft hole completely through so you can reverse the handle on the shaft when not in use, then it will not be so easy to bash your knee or leg when walking by.

Pain is a great teacher

Ken

[Don Young]

I found that the mating clutch part on the machine is readily available and not very expensive. It should be readily adaptable to make a hand wheel or crank.

Don Young

[uute]

So the dogs are just straight sided, from the pics I thought they were angled like a dovetail. Hence my strange reply above.

CT2

[Bguns]

Yes simple straight sides

Watched my machine shop teacher make one in minutes on a rotary table...

[Carld]

It appears to me in the photo that a line drawn from the side of each tooth would pass through the center line of the hole in the crank. If so why can't you machine along that line on each side of each tooth?

[LES A W HARRIS]

Couplings & Clutches

Machinery's Handbook, Couplings & Clutches.

Cheers,

[Frank Ford]

It appears to me in the photo that a line drawn from the side of each tooth would pass through the center line of the hole in the crank. If so why can't you machine along that line on each side of each tooth?

That's the deal - nine cuts 40 degrees apart and you're done.

[randyjaco]

Thanks for all of the replies. This was a real learning experience. I quickly learned that there are 2 offsets required and 2 different increments points of rotation. 14 total cuts at 51.4 degree increments is a little difficult to get exactly on my rotary table. I was really surprised to find that the OD of the cylinder makes considerable difference in the outcome. I made a test piece that was a diameter equal to the castellated hub shown in my original post. The test piece came out perfectly. The hub of the hand wheel was about a half inch larger in diameter. I presumed that this would make no difference on the index table using the same offsets and increments. WRONG The larger diameter caused the dynamics of the operation to change. The castellations decreased width at the contact points and the grooves increased in width. The end result was less than desired but still usable. Bummer

Thanks again

Randy

[A.K. Boomer]

Usually when looking at a part that's already been built it means that its already been through a simple process that can be duplicated, In this case the matching flats that intersect the center line ---- but if someone's already "screwed the pooch" and butchered their handle drive all they really have to do is mill it all flat, set up your R/T table or bolt hole calc. drill/ream and install some appropriate sized dowels, Don't be concerned about the unit pressure of the dowel rounds on the drive flats as these things are built with extreme overkill (probably enough to push your chevy down the road)
And if your a techno-weenie then just mill the receptor flats off too and drill the appropriate sized/spaced holes for the dowels, now you actually have a system that wont keep slipping off as your trying to raise or lower your table...

By the way -- if you get tired of your standard system slipping off while cranking you can set both the drive and the driven piece up with a slightly modified "bell bottomed" endmill (excuse the term - im not a machinist) and take some skin cuts, or tilt the head a couple degree's.
Now you have the same type of holding engagement design that your typical motorcycle transmission uses to hold in their gear engagement dogs, the more pressure the better the hold...