# What Happened to My Part?



## ddickey (Jun 1, 2017)

Starting a project and had to cut a 1.5" round to 3/8" and bore to .801".
Bore is spot on but when I measure the Ø I get .375 and .372 on the opposite side.
I wonder if when I parted it and returned it to the 4J if it did not go in square. I did bump it with a bearing on a holder and felt true. 
Any other reasons?
I'm going to take a face cut on a large piece before I redo the part.


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## Bill Gruby (Jun 1, 2017)

What am I missing in your first sentence? You said you turned 1.5 inches to .375 inches. Then you bored to .801?

 "Billy G"


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## ddickey (Jun 1, 2017)

.375 was the length of the part. Came from a 2" long bar.
1.5" is the OD.


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## markba633csi (Jun 1, 2017)

Ok so this part looks like a ring or washer and the faces are not parallel; instead they are off by 3 thou. Could be that the steps on your 4 jaw are not the same height. 
Could be a burr from parting off. Did you face again after parting? Or did you part to size?
Mark S.


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## ddickey (Jun 1, 2017)

I faced slightly after parting. Maybe five though.
Almost set up and ready to do it again.
I took a test cut on a 6" diameter round stock. It cut basically flat.


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## RJSakowski (Jun 1, 2017)

Squaring "pancake" type parts can be difficult. I usually square to a spacer.  The are three threaded holes for offset studs to square the spacer to the spindle axis.  Commerciaql versions are also available.


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## ddickey (Jun 1, 2017)

I would like to try and make something similar to what RobRenz did. Definitely would eliminate the problem.


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## woodchucker (Jun 1, 2017)

RJSakowski said:


> Squaring "pancake" type parts can be difficult. I usually square to a spacer.  The are three threaded holes for offset studs to square the spacer to the spindle axis.  Commerciaql versions are also available.


I have something similar, no jack screws. one is thinner than the other.


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## pdentrem (Jun 1, 2017)

You can use a dial indicator and write on the face of the part the high spot. Set the part in the chuck with the marked spot aligned with one of the jaws. Now the tricky part is to get the part set up with the dial indicator showing the correct readings of what you have. I have done this many a time with thin parts that are next to impossible to clamp against a stop.
Pierre


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## ddickey (Jun 1, 2017)

I'm rethinking now and believe it may have been my parting tool.
I use one of these,
http://www.eccentricengineering.com...mart&page=shop.browse&category_id=19&Itemid=3
This time, and maybe I should do this all the time, I indicated the blade. Normally I would use a square on the holder or post and square that to the chuck. Anyway, not sure why cause the clamping system is really proper but under the clamp the blade is straight but the part that is doing the cutting curves away from the center line. I only ever have just enough blade stick out to make the cut.
This time I parted to size and all is well.


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## woodchucker (Jun 1, 2017)

ddickey said:


> I'm rethinking now and believe it may have been my parting tool.
> I use one of these,
> http://www.eccentricengineering.com...mart&page=shop.browse&category_id=19&Itemid=3
> This time, and maybe I should do this all the time, I indicated the blade. Normally I would use a square on the holder or post and square that to the chuck. Anyway, not sure why cause the clamping system is really proper but under the clamp the blade is straight but the part that is doing the cutting curves away from the center line. I only ever have just enough blade stick out to make the cut.
> This time I parted to size and all is well.



I don't think that was it.
The only thing I think is if you removed the part and didn't square it up the part would be longer on one side and shorter on the opposite side.


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## pdentrem (Jun 1, 2017)

There is a lot of forces when using a parting tool. Likely the part moved just a bit, unless you hit near a hard spot and therefore the deflection?
Pierre


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## ddickey (Jun 1, 2017)

Could be. I got some chatter which I rarely do when parting with this tool. It came and went. Sort of odd.


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## epanzella (Jun 1, 2017)

I'm trying to picture your part. .375" long   1.5" od     .801 bore.   Why did you have to flip it in the 4 jaw? Couldn't it all be done with one setup?


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## ddickey (Jun 1, 2017)

I parted it a little so I could face it off to size.


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## epanzella (Jun 2, 2017)

ddickey said:


> I parted it a little so I could face it off to size.



Maybe this is what you're already saying, but, if I was making that part I would indicate it in the 4 jaw with about an inch of stickout, bore it to .810 about 3/4 deep, part in to 1 inch OD  (at bottom of hole),  face to length, (.375), and then continue parting right thru the bored hole. One setup and no worries about reinserting a short part out-of-square.


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## ddickey (Jun 2, 2017)

Thanks Epanzella.
What does the partial parting do?


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## Howardd (Jun 2, 2017)

RJSakowski said:


> Squaring "pancake" type parts can be difficult. I usually square to a spacer.  The are three threaded holes for offset studs to square the spacer to the spindle axis.  Commerciaql versions are also available.
> View attachment 234629


I'd be interested in the commercial commercial versions. What are they called?  Do you know who sells them?

Thanks 

Howard


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## RJSakowski (Jun 2, 2017)

Howardd said:


> I'd be interested in the commercial commercial versions. What are they called?  Do you know who sells them?
> 
> Thanks
> 
> Howard


Try looking for chuck stops.
https://www.mscdirect.com/product/details/00097584
http://www.travers.com/search.aspx?keyword=chuck+stop


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## woodchucker (Jun 2, 2017)

Howardd said:


> I'd be interested in the commercial commercial versions. What are they called?  Do you know who sells them?
> 
> Thanks
> 
> Howard


Mine is home made. I have seen them though. Check MSC


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## epanzella (Jun 2, 2017)

ddickey said:


> Thanks Epanzella.
> What does the partial parting do?


The partial parting locates one end of the part (closest to the chuck)  Then you measure from that groove to the other end of the part to get your .length. Leave it a bit long and then face it down to .375 from the groove to the end of the part. Go back and finish the parting and you're done.


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## ddickey (Jun 2, 2017)

Okay. Makes sense.


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## Wreck™Wreck (Jun 2, 2017)

If the parallel tolerance is critical as is denoted by this symbol on a drawing, in this case it does not indicate inches or millimeters..03MM is .0011xxx inches.



Holding this parallelism in a 3 jaw chuck will be tough sledding, pocketing soft jaws will help, if this is not an option part off and grind as a second operation.
Exactly what sort of accuracy are you looking for?


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## Wreck™Wreck (Jun 5, 2017)

Began a similar job today, 3.130" OD X .500 thick +- .003.
40 parts in 304 SS made from 3 1/4" saw cut round stock .6" long. Bored a pocket in soft jaws .125" deep X 3.25" Dia., faced and turned one half, flipped and turned the other half.

So far the first 10 parts were  <.001" out in thickness and parallelism and I was mildly surprised that turning the OD from both ends left no visible artifact, this I suspect will not last however.

This is the best option if you have to do this again in the future. If I were to remove the jaws then use them again 2 months from now I would skim cut them in place again, soft jaws are cheap.


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## ddickey (Jun 5, 2017)

Soft jaws huh? I'll have to check those out.


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## pdentrem (Jun 5, 2017)

I use a set of soft jaws as well. I have 2, 3, and 4" diameters cut into the face. I still get a bit of thickness error as the jaws were not loaded when they were cut.
Pierre


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