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Thread: Test Bar Suggestions
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26th January 2015, 03:59 PM #31.
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Stu,
I'm back to foot dragging. Alan and I established that the test bar has some run out. I need to spend some time with an indicator mounted properly to establish exactly how out of whack things are.
Alan does have a nice grinder Richard but having acquired scraping skills on the weekend, I imagine he'll be too busy scraping to want to fool around with the grinder.
An out of true tailstock is definitely going to drill an out of true centre hole. Point taken about the boring.
Kryn,
I'm pretty sure the fit of the tapers wouldn't be the problem. The arbors I have are made by Jacobs and Rohm though the Jacobs taper on one of my 2 Morse arbors appears bent. It and I reckon a number of my chucks have probably been the victims of crashes. While I do have a tool post grinder it's not going near my lathe. No matter how much trouble you go to trying to cover and protect the lathe from grinding dust, on a nine inch Hercus the dust finds its way into a cavity or crevice. The tool and cutter grinder might be up to the task if I could find a small enough internal grinding stone.
Bob.
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26th January 2015, 04:24 PM #32GOLD MEMBER
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Would you be able to borrow someone else's lathe to do it on . Someone you don't like, you could go there, when they're out and ask the wife if you could use his lathe .
The T&C grinder should be able to be set up to do it on, I would have thought.
Kryn
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26th January 2015, 08:25 PM #33.
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Kryn,
If I can devise a way to attach the TPG to the tool and cutter grinder, I would have the means to grind small diameter holes with bitty mounted wheels. The internal grinding spindle Hercus supplied for the No1 T and C, suits 1/4" bore wheels, not so bitty.
I made an elephant's foot for my metric threaded indicator from a piece of 316. I then mounted the "footed " indicator on the horizontal centreline. Mounting it vertically with some degree of accuracy is going to be a bit trickier.
It appears to me that the parallel section of the test bar is not concentric to the taper. The high point is in the same position at each end of the bar. The TIR is 0.02mm ( 0.0008" ) while the run out on the taper is 0.005mm ( 0.0002"). I installed a Hercus mill 10 inch arbor in the lathe's headstock spindle. At the unsupported outer end there was 0.02mm TIR. The test bar had nearly seven times that amount BUT it was sleeved to suit the headstock's 3 Morse bore. I find that sleeving can reduce ( if I'm lucky ) or exaggerate errors. In this case it's the latter.
BT
PS While I usually resort to smoke and mirrors to make you lot think everything is neat and tidy in my shed, these photos are honest. I have set the indicators on zero at the lowest point and photographed the error as indicated. I used the big Baty before because the tenth Interapid I had been using was, in some cases, rotating more than one full turn.
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26th January 2015, 08:52 PM #34GOLD MEMBER
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Nice looking holder for the indicator that goes in the tool holder. Thanks for reminding me, I need to make some myself.
I would have thought the T&C G would have the capability to do it, with out having to mount the tool post grinder to it.
Kryn
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26th January 2015, 09:07 PM #35GOLD MEMBER
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Hi BT,
Did you check run out on the small end of the taper?
Stuart
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27th January 2015, 11:30 AM #36.
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I slipped up to the shed for a bit more measuring and a few more photos.
Stu,
The small end of the test bar has about .004mm TIR but the high point is offset roughly 90 degrees from the high point at the large end. ( I haven't tried and I don't think it will fit but the 13's dividing head and tailstock mount on a saddle ensuring alignment. It would be ideal for checking the test bar between centres if it did fit.)
Kryn,
The photos below show the end of the Hercus T and C internal grinding spindle and the 11N and 8 1/2 N chuck's 2 Jacobs taper. The .4876" small end diameter is smaller than the wheel retaining screw on the spindle. The collet chuck is for the Dumore 44. The chuck has an internal mounting bore of 3/8" which won't fit the Hercus spindle without some destructive modification hence the suggestion of mounting the Dumore on the T and C. Here's a bit about the 44 - https://www.woodworkforums.com/showth...73#post1254573
A tiny Dremel chuck might be modifiable to suit mounting on the spindle nose. I'll have a look tonight.
Bob.
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