My little Lorch watchmakers’ lathe – about 100 years old - uses a small three-jaw scroll chuck. No doubt when new - given that the lathe was manufactured to turn small components to a high degree of accuracy (by the standards of the day) - I’ve no doubt that the chuck did run true. However, the ravages of time have taken their toll, and in any event 3-jaw self-centring scroll chucks aren’t noted for accuracy in centring stock, which is one reason that 4-jaw chucks prevail.
On larger items (in the context of a small lathe I mean up to 1.5” diameter), it isn’t too important, but recently, I needed to make some spindle couplers from ¼” diameter brass rod, drilled out to 3mm, so that the coupler could fit onto a 3mm diameter shaft, then a radio knob could fit onto the outside of the coupler. As the rod in the chuck oscillated from side to side, the 3mm diameter hole was not concentric with the outer diameter of the rod. Not enough to be immediately obvious to a casual observer, but enough to bug me. I therefore decided to try to correct this aberration.
I used a ‘dial test indicator’ (‘DTI’) to find out how far out of true the lathe was running. I inserted a ½” diameter brass bar into the chuck, and yes purists would say that a drawn brass bar isn’t necessarily perfectly round, but it measured round on a vernier. (I’m not putting rockets into space anyway – I’m just pottering around). The DTI showed that the bar was out of true by 0.2mm (about 8 thou of an inch).
Trying the easier options first, I completely dismantled the chuck and immersed in it my ultrasonic cleaner to remove all dirt and swarf from ‘the works’. It came out spotless, and when reassembled with a light coat of grease, it was a smooth as silk, but still not running true. Next, I removed the chuck from the backplate to check if the backplate itself was running true. (It was). There was absolutely no play in the mating surfaces of the chuck and backplate, so there was no prospect of centring it with very gentle taps with the hammer before finally nipping up the three bolts that hold the chuck to the backplate.
I removed and refitted the jaws several times just to make sure that the chuck was consistently out of true, and not just that play in the scroll and the jaws gave different results each time they were tightened. This gave the same results each time. The ‘out of trueness’ was biased toward jaw #1, which meant that jaws 2&3 were pushing the stock out of centre. The only option left was to carefully remove metal from jaws 2 & 3 on a diamond whetstone, always remebering that whatever material you take off on a lathe is twice as much on the diameter, so caution must prevail, especially when tinkering with irreplaceable long since obsolete items such as this chuck. I spent the best part on an hour removing a little at a time from the jaws, refitting and testing them. When I got it down to .08mm (3 thou), I decided to call it a day in a cold garage with numb fingers! I took a light cut off the brass bar on the lathe to see what improvement I'd made, and was content with the result. Not perfect by any means, but no longer bugging me.
I''ve attached a few pics to show the tests I carried out with the DTI, but I've moved it to get a clearer picture. When I did the measurements, the DTI was square on to whatever was being checked. Pictures 2 & 3 show the two dial readings to illustrate the extent to which the chuck was out of true, with the tip of the DTI on the brass bar in the chuck. (0.2mm - about 8 thou). The other two pics of the DTI show how I checked that the backplate, and the assembled chuck, were both running true,
For old fogeys like me brought up with imperial measurements, I try to use metric, but when it comes to fine tolerances, I regress back to childhood and have to think in ‘thous’. Basically, 'I live in my own little world', but that's OK...they know me here!
I find that this comes in handy:
http://www.metric-conversions.org/length...inches.htm
Footnote: DTIs on an adjustable stand with a magnetic base, such as the Silverline ones, suitable for hobbyists like me are cheap enough - typically £15.00 or a bit less, often with free P&P. EG:
http://www.amazon.co.uk/Silverline-59845..._2?ie=UTF8&qid=1356112726&sr=8-2-spell
The dial reads down to 0.01mm, which is 0.00039370 of an inch. The magnet is extremely powerful and can be turned on or off. (No electrics involved – all done by smoke and mirrors!).
The base has a ‘V’ shaped groove to allow it to be clamped to round objects as well as say a flat lathe bed and there are fine adjustments to help set it up as needed. They seem to get good reviews.
Any lathe of advanced years that has passed through many hands will have suffered neglect and abuse, (a glance at the offerings on e-bay will provide ample evidence of that). Hence we have to learn to live with such imperfections as arise, doing the best we can to 'tune up' the lathe to our level of skill and what we wish to turn on the lathe, which in my case, is really quite basic on both counts. There are of course those who know the price of everything and the value of nothing so would just buy a good quality new lathe, but if I were to do that (as I could), it would spoil the fun, in rather the same way that buying a new car would be a turn off for a vintage car enthusist. Which is why me and my little Lorch get along fine together.
Hope that may be of interest to fellow novice turners or would be lathe owners.
On larger items (in the context of a small lathe I mean up to 1.5” diameter), it isn’t too important, but recently, I needed to make some spindle couplers from ¼” diameter brass rod, drilled out to 3mm, so that the coupler could fit onto a 3mm diameter shaft, then a radio knob could fit onto the outside of the coupler. As the rod in the chuck oscillated from side to side, the 3mm diameter hole was not concentric with the outer diameter of the rod. Not enough to be immediately obvious to a casual observer, but enough to bug me. I therefore decided to try to correct this aberration.
I used a ‘dial test indicator’ (‘DTI’) to find out how far out of true the lathe was running. I inserted a ½” diameter brass bar into the chuck, and yes purists would say that a drawn brass bar isn’t necessarily perfectly round, but it measured round on a vernier. (I’m not putting rockets into space anyway – I’m just pottering around). The DTI showed that the bar was out of true by 0.2mm (about 8 thou of an inch).
Trying the easier options first, I completely dismantled the chuck and immersed in it my ultrasonic cleaner to remove all dirt and swarf from ‘the works’. It came out spotless, and when reassembled with a light coat of grease, it was a smooth as silk, but still not running true. Next, I removed the chuck from the backplate to check if the backplate itself was running true. (It was). There was absolutely no play in the mating surfaces of the chuck and backplate, so there was no prospect of centring it with very gentle taps with the hammer before finally nipping up the three bolts that hold the chuck to the backplate.
I removed and refitted the jaws several times just to make sure that the chuck was consistently out of true, and not just that play in the scroll and the jaws gave different results each time they were tightened. This gave the same results each time. The ‘out of trueness’ was biased toward jaw #1, which meant that jaws 2&3 were pushing the stock out of centre. The only option left was to carefully remove metal from jaws 2 & 3 on a diamond whetstone, always remebering that whatever material you take off on a lathe is twice as much on the diameter, so caution must prevail, especially when tinkering with irreplaceable long since obsolete items such as this chuck. I spent the best part on an hour removing a little at a time from the jaws, refitting and testing them. When I got it down to .08mm (3 thou), I decided to call it a day in a cold garage with numb fingers! I took a light cut off the brass bar on the lathe to see what improvement I'd made, and was content with the result. Not perfect by any means, but no longer bugging me.
I''ve attached a few pics to show the tests I carried out with the DTI, but I've moved it to get a clearer picture. When I did the measurements, the DTI was square on to whatever was being checked. Pictures 2 & 3 show the two dial readings to illustrate the extent to which the chuck was out of true, with the tip of the DTI on the brass bar in the chuck. (0.2mm - about 8 thou). The other two pics of the DTI show how I checked that the backplate, and the assembled chuck, were both running true,
For old fogeys like me brought up with imperial measurements, I try to use metric, but when it comes to fine tolerances, I regress back to childhood and have to think in ‘thous’. Basically, 'I live in my own little world', but that's OK...they know me here!
I find that this comes in handy:
http://www.metric-conversions.org/length...inches.htm
Footnote: DTIs on an adjustable stand with a magnetic base, such as the Silverline ones, suitable for hobbyists like me are cheap enough - typically £15.00 or a bit less, often with free P&P. EG:
http://www.amazon.co.uk/Silverline-59845..._2?ie=UTF8&qid=1356112726&sr=8-2-spell
The dial reads down to 0.01mm, which is 0.00039370 of an inch. The magnet is extremely powerful and can be turned on or off. (No electrics involved – all done by smoke and mirrors!).
The base has a ‘V’ shaped groove to allow it to be clamped to round objects as well as say a flat lathe bed and there are fine adjustments to help set it up as needed. They seem to get good reviews.
Any lathe of advanced years that has passed through many hands will have suffered neglect and abuse, (a glance at the offerings on e-bay will provide ample evidence of that). Hence we have to learn to live with such imperfections as arise, doing the best we can to 'tune up' the lathe to our level of skill and what we wish to turn on the lathe, which in my case, is really quite basic on both counts. There are of course those who know the price of everything and the value of nothing so would just buy a good quality new lathe, but if I were to do that (as I could), it would spoil the fun, in rather the same way that buying a new car would be a turn off for a vintage car enthusist. Which is why me and my little Lorch get along fine together.
Hope that may be of interest to fellow novice turners or would be lathe owners.
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
