jem
Elder Statesman
Posts: 1,066
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Post by jem on May 12, 2018 16:10:16 GMT
Hi,
Yes very interesting, but why do you have the tool at 40 degrees please? I made some boring bars many years ago, and put the HHS bits at 90 degrees to the bar, I also put a threaded hole next to the tool,with a headed screw in it so that I could advance the bit by turning the screw. This has worked very well for me. so I am all ears for your design.
best wishes
Jem
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Post by goldstar31 on May 12, 2018 18:45:14 GMT
Again, I would suggest that you read Thomas and the 40 degree angle and 40TPI achieves the 'Gnat's C***" advance
He also pronounced on the set over of the top slide to get thous.
Pity GHT wasn't around any more as I also have a ==== shhhhhhhhhhh!!! Metric lathe! C
Regards
N
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rrmrd66
Part of the e-furniture
Posts: 339
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Post by rrmrd66 on May 13, 2018 6:54:19 GMT
Hi, Yes very interesting, but why do you have the tool at 40 degrees please? I made some boring bars many years ago, and put the HHS bits at 90 degrees to the bar, I also put a threaded hole next to the tool,with a headed screw in it so that I could advance the bit by turning the screw. This has worked very well for me. so I am all ears for your design. best wishes Jem Hi Jem
GHT's idea ref 40deg for the tool angle was to ensure that there was an uncluttered potion of boring bore diametrically opposite the tool tip over which to measure the amount of tool protrusion with a micrometer.
By applying that simple formula you arrive at the diameter of the bore, about to be machined, for that particular setting.
He also suggested it helped reduce a possible weakness in the bar had he have used 45deg. Not too sure about that one?
The tool is advanced by turning the M8 dog point screw. In an ideal world you would probably use an ME 40tpi thread giving 0.025" forwards movement per complete turn (just like an imperial mic').
I hate stopping work to go on a 13 mile round trip to my local ME parts supplier for one screw and had the M8 dog point socket head screw was to hand (also the taps). This gave me approx 0.012" per quarter turn.
I filed four x 90deg nicks in the end of this adjustment screw and filled them with Tippex (so that i could see the amount turned) to reference against a mark on the bar. Not quite GHT but good enough. There was something like 0.200" to remove from the diameter of the cylinder casting, so enough to play with.
GHT's design is naturally quite detailed with a very different tool advance mechanism although he does suggest a simplification which I partly adopted.
Hope this all makes sense?
The cylinder bores are finished now and I will write up about all of this in my 5"gauge Hunslet build thread in due course.
cheers
Malcolm
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Post by goldstar31 on May 13, 2018 7:46:01 GMT
Good Morning Malcolm( and Jem)
Thank you for the 'Like;
I'm really getting on in years(87+++)and with macular degeneration and a fitful memory but I THINK thaT GHT used the 40 degree angle on his inline boring bars to use them as micrometers as he used a 40TPI thread to advance his cutting tool. Being somewhat also pedantic, mine is made that way. It was for a Quorn which has parallel bores linking the three castings but goes up from a bore of 1.000" in the first two castings but increases to 1.003" in the final one.
It's is not pedantic without a reason as a split bore can close up and nip. Oh, yes, guess how I know!
Returning to the micrometer thing in - an Imperial lathe- GHT continued his advice in setting a Myford top slide at 20 degrees so that it would take a 'tenth of a thous' off instead of a guessed thous.
I think that my memory is still 'holding up'
As I said, I also have aa SiegC4 which -- could do with someone like GHT but with a metricated mind.
So my kind regards to you both whilst you wrap a towel around your heads and take copious supplies of pain killers
Norman
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jem
Elder Statesman
Posts: 1,066
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Post by jem on May 13, 2018 19:01:47 GMT
Thank you very much for the detailed explanations, most interesting. I will certainly give this a try when I make my next boring bar. Norman would pain killers be beer or wine?
best wishes everyone
Jem
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