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+--- Thread: Rebore on a mini-lathe!!! (/showthread.php?tid=2084)
RE: Rebore on a mini-lathe!!! - Austin in the Shed - 08-12-2018
I've never done rebores,Well ,only once to 60mm which lasted about 150 miles before the side fell out of one of the bores.But from the people who do they bore slightly undersize and get the cross hatch finish and size by honing.
I do sometimes still screwcut threads by hand as it's easier than trying to stop/reverse the motor each cut.A tip an ex Myford employee and friend gave me.
RE: Rebore on a mini-lathe!!! - Reckless Rat - 08-12-2018
Cutting threads (imperial) on the Myford doesn't involve having to stop or reverse the motor, although to do it your lead screw has to be fitted with the thread indicator accessory. Cutting METRIC threads however does involve reversing or rewinding the lead screw manually because if you disengage you lose the correct mesh. This is due to metric thread gauges being different from imperial. HTH.
B
RE: Rebore on a mini-lathe!!! - bob46320 - 08-12-2018
(08-12-2018, 02:16 PM)Reckless Rat Wrote: Cutting threads (imperial) on the Myford doesn't involve having to stop or reverse the motor, although to do it your lead screw has to be fitted with the thread indicator accessory. Cutting METRIC threads however does involve reversing or rewinding the lead screw manually because if you disengage you lose the correct mesh. This is due to metric thread gauges being different from imperial. HTH.
B
Bruce, it depends wether you have a Myford with an Imperial or Metric leadscrew. Imperial threads and imperial leadscrew, use the thread indicator, Imperial threads and Metric leadscrew (using the conversion gears) you would need to reverse the motor etc for each cut.
Cribbed from Home Machinest:-
Even number threads can be engaged on any line or numbered line. Odd threads can be engaged on any numbered line OR on any line. For odd numbered threads, once you start with numbered lines you can only use any numbered line and the same is true if you start by using the non-numbered lines. For 1/2 numbered threads and 1/4 numbered threads such 11-1/2 or 4-1/4 it is easiest to remember to use the exact number or mark for each engagement.
Bob
RE: Rebore on a mini-lathe!!! - Reckless Rat - 08-12-2018
Ferzackerly what I meant to say mon pôte.
RE: Rebore on a mini-lathe!!! - Ruairidh Dunford - 10-12-2018
(08-12-2018, 12:57 PM)Ruairidh Dunford Wrote: On the wall of my father's workshop is a hand operated boring bar that a man in the village made to re-bore his Austin during the war.
It is beautifully made but we reckon it would take a day a bore!
My father writes:
"Here are photographs of an Austin Seven cylinder boring tool made during the war at The Bristol Aeroplane Company by the father of a friend of mine in Frampton.
It was made to bypass the wartime problems for private A7 owners.
I was shown how it worked 40 years ago and the only memory I have is of exhaustion."
RE: Rebore on a mini-lathe!!! - Dave Mann - 10-12-2018
I wonder what bit of a Bristol plane those gears came from Ruairidh? Any slop in that bearing will produce a bore tapered the opposite way to normal.
RE: Rebore on a mini-lathe!!! - Stuart Giles - 10-12-2018
That's an interesting piece and a really interesting story too. With the amount of company time and material that probably went into that "Homer" it might have have been cheaper for the company to have bought the bloke a brand new block, or at least let him rebore his own on one of the probably numerous horizontal boring machines that would have been in place at the factory back then.
The workshop where I spent a lot of my apprenticeship had the benefit of a manager who wouldn't have been able to interpret a drawing if his life depended on it, so some of the "industrial printer components" I was machining from EN8 billet came out remarkably like bits for the 500 Triumph motorbike I used for work before I bought my A7 Special.
RE: Rebore on a mini-lathe!!! - Zetomagneto - 10-12-2018
(10-12-2018, 09:55 PM)PStuart Giles Wrote: That's an interesting piece and a really interesting story too. With the amount of company time and material that probably went into that "Homer" it might have have been cheaper for the company to have bought the bloke a brand new block, or at least let him rebore his own on one of the probably numerous horizontal boring machines that would have been in place at the factory back then.
The workshop where I spent a lot of my apprenticeship had the benefit of a manager who wouldn't have been able to interpret a drawing if his life depended on it, so some of the "industrial printer components" I was machining from EN8 billet came out remarkably like bits for the 500 Triumph motorbike I used for work before I bought my A7 Special.
Nicely constructed, but doubt if it improved the block as I cannot see how it would have produced
a parallel bore.
RE: Rebore on a mini-lathe!!! - Austin in the Shed - 11-12-2018
Does the cone on the end locate the bottom of the bore as a guide ?
RE: Rebore on a mini-lathe!!! - Ruairidh Dunford - 11-12-2018
As noted above - it was last turned around 40 years ago Dave, but yes, I think you are quite correct.
The man who designed and made it was able to make it work successfully, which has always impressed me.