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#3349379 - 04/21/14 06:27 PM Re: Q for Machinist [Re: expat]
sleddriver Offline


Registered: 02/06/10
Posts: 1800
Loc: Central Texas
I understand your point, force across a larger surface.

It's easy enough to try pressing the coupler onto the motor shaft since the splines are so short and then filing a round hole square. I can always shim with a beer can if it's a bit too large. I'll practice in scrap first.

I'll have some time this evening to work on it.
_________________________
1998 Volvo V70 T5 200,771 mi. Original Owner.

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#3350635 - 04/22/14 10:17 PM Re: Q for Machinist [Re: sleddriver]
sleddriver Offline


Registered: 02/06/10
Posts: 1800
Loc: Central Texas
Update:

This evening I finally got it together....but made a mistake. More on that later.

I chucked my nylon plastic part into a vise, and marked four corners on the face. Then took a small, square needle file and made some grooves on each one, working up inside the bore.

Next, I held the shaft with a vise, set the plastic end on top and whacked it with a hammer. After a few times, I managed to fully seat the shaft into it. I can see where the metal corners of the shaft 'forced' the plastic to yield as I drove it home, creating four lines 90 apart. Didn't look like it would ever give.

I turned to the motor shaft end. I'd underbored it to be safe, then searched for a 9/32" drill with no joy. The OD of the shaft I'd previously measured at 0.3". A 9/32 is 0.28". 17/64 is 0.27. Unfortunately, I had neither.

Then I found a pen tool reamer that was very, very close to 9/32 so I thought "Why not"? It wasn't exactly straight though and was enough to widen it a fraction over what was necessary.



I tried it out with the string trimmer attachment and it worked for about 15sec., then I could hear the motor side of the coupler slipping. Sure enough, it was loose. @#$%!

I decided to cut a piece off of some 3/4" AL plate. It sure was slow going with a hack-saw. Then I spied a piece of 1" square Corian and thought of trying that. (I'm out of 1" round Delrin). However, the 3-jaw Taig chuck wouldn't hold the square Corian and I don't own a 4-jaw chuck.

So I marked and drilled the center to slide it onto my pen mill to turn it down to 3/4" round. The Taig was cutting very well and I had fine whisps of Corian flying right off of the tool.

Only then did I think to check if the drilled center was too large for the square end.....yep! Screwed the pooch on that one.

So I've decided to hang it up until tomorrow when I can get to the local HW store that carries drills in No. sizes. Even if the bore wasn't too large for the square end, I still wouldn't have an appropriate sized drill for the spline-end. And the dia. is too small for my inside boring tool. A more experienced machinist could figure this out, but I'm just a beginner.

It did occur to me that I could file a flat on the motor shaft, and drill my coupler for a set screw or two. Not sure so I've vetoed that for now.

I'll also have to deal with the assembly of order if I'm to press-fit both the flex shaft AND the motor shaft to the coupler. One is very easy because I can tap the end of the coupler, the other though requires me to set the motor upright on the bench, position the coupler and upper drive-shaft in place, then tap the end of the flex shaft to seat it into the coupler.

Any advice?
_________________________
1998 Volvo V70 T5 200,771 mi. Original Owner.

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#3350736 - 04/23/14 01:37 AM Re: Q for Machinist [Re: sleddriver]
expat Online   content


Registered: 05/12/09
Posts: 3824
Loc: Canada
Give up the Plastic.
Try Brass or Aluminum.

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#3352000 - 04/24/14 02:00 PM Re: Q for Machinist [Re: sleddriver]
sleddriver Offline


Registered: 02/06/10
Posts: 1800
Loc: Central Texas
SUCCESS!!

Joy finally arrived yesterday! With both a 17/64 and 9/32 drill in hand, I sought to machine another coupler to replace the end I'd over-bored.

I cut a block of 6061 AL, but then encountered the same problem of holding a four-sided square in a three-jawed chuck. I thought of belt-sanding off the corners, but it still wouldn't be round. Unable to locate round AL or brass rod yesterday.

So I took another eye at the Corian I'd milled. Decided to try out my new bits on it. Discovered it doesn't like to be press fit! Even 1/64" undersized. It cracked along its length as I tapped the motor shaft into the end.

I then spied the 2" black delrin rod as a better option than getting stuck in late afternoon traffic, driving to a friends house 15mi away who did have metal rod.

I turned down the delrin rod to 0.65. This stuff just machines beautifully! One, continuous thin stream pealing off the tool, into the air. From this it was obvious the white plastic I'd used earlier wasn't delrin. HDPE perhaps. No tapers this time. For the square hole, I again marked the corners with a knife, filed a notch at each with a square needle file and then used a countersink to ease the transition into the hole.

On the opposite end, I started the hole with a small end mill then worked up a few sizes. 17/64 may have worked. I wasn't worried about the delrin cracking. But I went 1/64" further with the 9/32 bit. Countersinked this hole as well and champhered both ends with a 45 tool.

I carefully seated both ends, reinstalled and attached the weed eater tool for a test. SUCCESS! It ran for about 15s without a hitch. Tried it again on HI. Joy.

Reassembled the motor cover and went to test it with some weed-wacking. Did both the front & back yards without a problem!

YESSSSS!

Wow...was I clam-happy! Even blew through some tough weeds on HI power. Sounded the same as before.

I don't have a completed coupler pic. Too excited to try the thing out. Besides, I've taken this thing apart > 20 times in the past several weeks.

So far, so good. I'm looking fwd to plugging in the mini-tiller attachment to check its functioning soon.

When I do acquire the rod, I'll save it in case this one goes Tango Uniform. I've learned quite a bit here and enjoyed spinning a new part. I wish 1" AL & brass rod were easier to obtain.

Thanks to all who pitched in for suggestions!
_________________________
1998 Volvo V70 T5 200,771 mi. Original Owner.

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#3352392 - 04/24/14 10:49 PM Re: Q for Machinist [Re: sleddriver]
tom slick Offline


Registered: 05/26/03
Posts: 8594
Loc: Central Coast, Calif.
Glad you got it figured out. You are correct, Delrin machines nicely, HDPE is a pain to machine.
_________________________
You get what you pay for...
So keep in mind how much you paid for this advice.

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