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Smart and Brown Lathe Crosslide Screw Renewal
John Stevenson:
What about using the phossie nut you have made and then using a Delrin nut spaced out from the phossie one with those dished washers.
That will provide zero backlash without relying solely on a soft Delrin nut.
You can make spare up at the same time for replacements down the line.
The dished washers will keep a preload on the whole shebang.
Just guessing here as i don't know the build up on a Smart and Brown lathe
John S.
Darren:
Hi John, interesting idea, but not sure it will work in this case due to the design of the machine.
Thanks
Darren
Darren:
Wow, this one had to have the cobwebs blown off..... :lol:
Well a little more progress today, first to make the backlash nuts shown in this picture from the SS bar end below the two nuts.
Roughed out with and old tip in the funny orientation holder to use the "other two" cutting edges.
Final shape with a new tip. I'm just putting a groove in for the friction spring that tensions the indicator dial.
Drilled,counter drilled part way and tapped 8mmx1.25.
The original was 3/8 with a 20tpi thread. 20tpi is almost 1.25mm metric pitch, so I chose an 8mm thread as the pitch was more important than the diameter...
I also threaded the leadscrew 8mm at the handle end by single pointing on the mini lathe as i don't have an 8mm die. Sorry forgot to take pictures of this :doh:
Set up in a 5C collet fixture to drill a 3mm hole for the locking pin of these two parts.
Counter sunk with a 6mm spotting drill and then turned a 3mm brass pin. I chose brass in case I ever wanted to take it apart. Easier to drill a soft brass pin out than a hard steel one.
Also brass would be easier to beat into the countersunk areas to secure it.
Now beaten into place. The pin should also swell inside the hole to make a nice tight fitting.
This is how it all fits together. You can see the old two backlash adj nuts in the bottom of the picture. They have holes in them to insert a bar to open and close them for adjustment.
Firstly they can be rather tight, and with a small bar (drill bit) it can be very difficult to undo them. Secondly the drill bits usually bend :doh:
Thirdly the holes become distorted in time making them useless....
So what to do? Mill two flats for a spanner fitting, drill similar holes but make a pair of proper bars, say a short 4mm diameter to fit the nuts and then expand to 6mm or more. Would be easier to use than drill bit :ddb:
Or something else, any suggestions welcome...
John Stevenson:
Slots and a C spanner ?
John S.
Darren:
Thanks John, I did consider that but the thought of making a c-spanner has put me off. I'll prob go for simple holes but make a proper fitting pair of keys/bars. Should cause less damage that way I think.
Indecently, I recently bought a Drill Doctor drill sharpener and this is the first real chance I have had to test the results. I'm happy to report that the sharpened bits drill better than some new ones I have, seem smoother. But the split points that this unit is capable of producing is a real eye opener. You can push a 10mm bit through a SS bar as if it was a 5mm bit with no smaller counter bore hole or center drill first.
I'm really impressed with the sharpening results.
I have re-sharpened about 200 drill bits so far so I consider it already paid for. Also I sharpened some snapped drill bits to make some stub drills to benefit from the extra rigidity.
A tool worth having IMHO....
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