5C Collet Slide Mount for Lathe Faceplate

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seal killer
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5C Collet Slide Mount for Lathe Faceplate

Post by seal killer » Thu Sep 20, 2012 11:35 am

All--

I like to build little steam engines with one-piece crankshafts. I have built a total of 1.5 of them. :) My trials and tribulations are well documented in several threads on this site. ONE of my issues concerns holding the small diameter crankshaft work pieces in my 8" Chinese 4-jaw chuck. I have to shim the jaws to reduce the run out acceptably. (Doing that was a good learning experience.) The small diameter of the work piece, 3/4", makes it difficult to hold reliably; the work piece slips and that's the end of that. If I tighten it so it to the point it will not slip, the jaws mark the work piece (unless it is protected by soft shims.)

How do you get around these problems?

BadDog suggested a 5C collet fixture. I bought one. (Thanks, BadDog!) Before it arrived, I knew I would have to build a plate to mount it across my 11" lathe face plate. That got me to thinking about building a precision mounting fixture for the 5c collet fixture. My efforts and some issues are shown below.

I used 1018 throughout. The "back plate" (got a better name for it?) is from 3/4" x 6" stock. I milled a 3/8" x 4.5" slot and used a t-slot cutter to create t-slots on both sides of its width. (I'm not sure if I wrote that last part correctly.)

The slide mount plate is a piece of 1/2" x 4.5" stock. I milled shoulders (?) on both sides to fit in the wide t-slot created in the back plate. For "precision" positioning, I used a captured 5/16-24 SHCS. The central holes you see in both the back plate and the slide mount plate are unnecessary and I will not include them on the NEXT one, should I decide to build another to fix all my mistakes.

I messed around trying to align this thing for a bit. And then some more. Finally, I stuck a short 3/8" pointy thing in my tail stock mounted drill chuck and ran the tail stock up to the loose 5C collet fixture with a 3/8" collet inserted. This got me very close (two or three thousandths) and I put the final alignment on it using the alignment screw for one axis and a little prying using some not-shown bolts mounted through the face plate for the other axis.

This device solves three problems for me . . .

1. The collet fixture will not mar the work piece.
2. The work piece will not slip as it did in the 4-jaw.
3. Shimming is not necessary.

However, although the run out of this device is far less than my 4-jaw, it still exists. At 7/8" from the collet face (about as close as I could easily get), the run out is about 0.0015". At three inches, the run out is 0.0035". This is acceptable for my purposes. But, it bugs me! How can I reduce it?

One thing I did NOT do during machining was pay attention to stress relief while creating the wide slot in the back plate. I'm not sure how I would have done that. (Maybe a little tiny fly cutter?) The slide plate was machined without regard to making the front and back sides parallel . . . I "trusted" they would be parallel since they are SUPPOSED to be parallel. (If I rebuild it, I won't make that mistake again.)

I am thinking about putting three adjustment screws in the face of the slide plate in a tripod arrangement. My guess is that as little as 0.0005", more or less, would make a big difference out at three inches from the collet face. What do you think about that idea? (The picture in the NEXT post shows where I am thinking about putting the adjustment screws. I marked the spots with red dots.)

The back plate is held to the lathe face plate with four automotive 3/8-16/24 studs. The slide mount plate is held to the back plate by the t-slot. When the correct position is dialed in, the slide mount plate is then clamped to the back plate with four 3/8-16/24 automotive studs. The 5C collet fixture is held to the slide mount plate with 1/2-13 studs.

I will balance the entire thing by bolting weights in the appropriate places to the lathe face plate. I would appreciate your thoughts on any aspect of this project.

Run out video 7/8" from collet face.

Run out video 3" from collet face.

--Bill
Attachments
09-14-12_5c_Slide_Mount-a.JPG
Back Plate
09-14-12_5c_Slide_Mount-b.JPG
Slide mount in foreground.
09-14-12_5c_Slide_Mount-c.JPG
Assembled device.
09-14-12_5c_Slide_Mount-d.JPG
Assembled device with 5c collet fixture mounted.
09-14-12_5c_Slide_Mount-e.JPG
Precision 5c collet slide mount on lathe face plate.
You are what you write.

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seal killer
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Re: 5C Collet Slide Mount for Lathe Faceplate

Post by seal killer » Thu Sep 20, 2012 11:36 am

All--

Potential adjustment screw positions.

--Bill
Attachments
09-14-12_5c_Slide_Mount-e-reddots.jpg
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Richard_W
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Re: 5C Collet Slide Mount for Lathe Faceplate

Post by Richard_W » Thu Sep 20, 2012 12:59 pm

Your video suggests that the center line of your collet vise isn't a perfect 90 degrees to the base. Would a shim under one end fix the problem and be good enough or recutting the base?


Richard W.

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seal killer
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Re: 5C Collet Slide Mount for Lathe Faceplate

Post by seal killer » Thu Sep 20, 2012 1:57 pm

Richard--

Are you seeing something in the video that I missed? The lamp on the lathe reflecting off the end of the indicated drill rod makes it look like it's wobbling.

--Bill
You are what you write.

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ctwo
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Re: 5C Collet Slide Mount for Lathe Faceplate

Post by ctwo » Thu Sep 20, 2012 2:17 pm

That could be from the collet vice as Richard suggests or maybe the adapter plate does not have parallel sides. Did you indicate the plate after mounting?
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To measure is to know - Lord Kelvin
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Richard_W
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Re: 5C Collet Slide Mount for Lathe Faceplate

Post by Richard_W » Thu Sep 20, 2012 2:20 pm

seal killer wrote:Richard--

Are you seeing something in the video that I missed? The lamp on the lathe reflecting off the end of the indicated drill rod makes it look like it's wobbling.

--Bill
Your indicator readings shows increased run out at 3" which tells me the centerline of the collet vise isn't perfectly on center to the lathe spindle center line. Meaning the base of the collet vise isn't true to the collet or the face plate runs out a bit. The other possibility is your slide fixture has a taper on one or more parts. Other-wise the shaft would have a zero reading no matter how far you had the shaft hanging out. Unless of course the collet is at fault?

Most likey doesn't matter for a crank throw as the run out would almost be non-existant for such a short journal.

Richard W.

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seal killer
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Re: 5C Collet Slide Mount for Lathe Faceplate

Post by seal killer » Thu Sep 20, 2012 2:53 pm

Richard and ctwo and All--

Richard, aaah. Yes. I agree. That is why I am contemplating those three adjustment screws shown in red, above. I don't have enough experience to know if they might work, though.

ctwo, no, I did not indicate either plate after mounting. I DID indicate the top of the collet fixture after I mounted it, though. It was 0.0005" out. Ideally, it should be in the same plane as both plates. I am thinking that 0.0005" translates to the 0.0015" you see at 7/8" and the 0.0035" you see at 3" out. What do you think?

--Bill
You are what you write.

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ctwo
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Re: 5C Collet Slide Mount for Lathe Faceplate

Post by ctwo » Thu Sep 20, 2012 3:22 pm

Mr. Killer,

I'm not sure if the front face of the vice is that accurate to the collet axis. If it were, and if your measured runouts were all coincident (are they?), then there could be correlation. Then, all that's telling you is that the vice is not mounted square/parallel with the spindle axis.

Let's assume that is the case and that the diameter that you indicated is 2". That means there would be 2.5 thenths runout per inch, and that does not correlate with your measured runout at 7/8 nor at 3"... as a matter of fact, your measured runout does not appear to be linear, which it would if everything else was perfect.

i.e., your measured runout is:

0.0015 per 0.8750 = 0.0017 per inch
and
0.0035 per 3.0000 = 0.0012 per inch

OK, that is within the tolerance of the measuring equipment, I'm sure...

To track this down, you'd need to carefully indicate more surfaces and verify the surfaces on your vice for squareness/parallelism... you might be able to do that if you have a surface plate...?
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

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seal killer
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Re: 5C Collet Slide Mount for Lathe Faceplate

Post by seal killer » Thu Sep 20, 2012 9:47 pm

ctwo--

Thanks for the explanation. I will put a DTI on it and see what I REALLY come up with.

--Bill
You are what you write.

Inspector
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Re: 5C Collet Slide Mount for Lathe Faceplate

Post by Inspector » Fri Sep 21, 2012 3:57 am

Bill you need to start from the faceplate and work your way out to discover which parts are giving you the problem. Assuming the faceplate indicates true, if you mount the collet chuck directly to the faceplate and it indicates correctly then your fixture is out and needs the "set tru" screws or other rework to correct. If the collet chuck on faceplate doesn't indicate correctly then it is the collet chuck that's out and the rework needs to start there.

I will add that is a heck of a good eccentric chuck setup you are putting together.

Pete

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Lew Hartswick
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Re: 5C Collet Slide Mount for Lathe Faceplate

Post by Lew Hartswick » Fri Sep 21, 2012 7:35 am

I haven't needed one yet, but that looks like a slick solution to the problem if it occurs. :-)
...lew...

Mr Ron
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Re: 5C Collet Slide Mount for Lathe Faceplate

Post by Mr Ron » Fri Sep 21, 2012 10:13 am

Beautiful work. My impression is there are too many "layers". A couple of tens out on the flat surfaces can add up to an overall runout in the thousands. The collet may be out, the collet fixture may be out, the lathe spindle may be out. A 10th here, a 10th there adds up. I may be wrong, but that's my impression.
Mr.Ron from South Mississippi

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