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5th Nov 2019, 04:38 PM #16Diamond Member
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- Revesby - Sydney Australia
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Fixed! Solved! Free!!!
OK. After getting the thing off again (required wedges, locking with back gear, and a blowtorch's heat!!!), I took the plate off the chuck and looked more carefully.
• One side of the threads – the headstock side – was good.
• The chuck side has some raised marks near the peak of the thread (crest).
Looked like judders from original machining. I did my best to hand scrape that out.
• There is slight wear on the shoulder/register touching surface.
I tried filing, then lapping with a small stone.
Oiled it up and hand fitted again. Smooth until it hits the shoulder/register on the spindle, then effectively locks on. Also tried mounting back to front. Stops about half a turn on. Must be tapered.
My machinist neighbour had a feel, and said it seems to touch, then go in a little further. Suggested I take a few thou off that side. Had to use his lathe because faceplate won't mount backwards. Did my best to mount it flat. First facing cut showed about 5 or 6 thou wobble. Hoped that wasn't my poor mounting. Faced it flat.
Oiled it up and tried on my spindle again. Was a little easier to remove, but of course there was now wobble on the chuck side. Looked carefully. It seemed like the oil that oozed out around the shoulder/register was uneven. Oh no. Did I mount & machine it badly? Damn. Should have used a dial indicator.
Took it off, thought about re-facing in the bigger lathe, but changed my mind and just faced in mine.
After wiping off a million little iron chips, re-mounted the chuck, and turned down something tough to give it some mechanical shock (4040 with Tungsten Carbide).
OK. Now to try taking off.
- Tried to remove chuck by hand (just gripping the pulleys by hand). Failed.
- Locked back-gears, and tried to remove with both hands. It spun free!!!
So, it seems like the slight wear on the mating surface – and not the thread – was causing the sticking.
Maybe it was wringing from the super-polished surfaces!
(caused by air pressure, surface tension, molecular attraction?)
It will be interesting to see what happens after the freshly faced Iron surface becomes a bit more polished. Time will tellLast edited by nigelpearson; 5th Nov 2019 at 04:44 PM. Reason: better grammer
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6th Nov 2019, 06:58 AM #17Mechanical Butcher
- Join Date
- Oct 2004
- Location
- Southern Highlands NSW
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- 1,898
Do you have clearance between the cylindrical surfaces beyond the threads, near the flat face?
Both my Hercus lathes have a gap at this place. That is, they don't touch. It's evidently how Hercus made them.
Or rather, how they finished the chucks, faceplates, backplates.
There is no larger diameter beyond the spindle thread, as often seen on other lathes.
Could be you have a too-close fitting faceplate that is causing your problem?
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6th Nov 2019, 09:06 AM #18Diamond Member
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- Aug 2019
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- Revesby - Sydney Australia
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Unbolt chuck, have a look. About 3/32" clearance:
IMG_0287.jpg
(and, just for interest's sake, unscrew and photograph the other side)
IMG_0288.jpg
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6th Nov 2019, 06:28 PM #19Mechanical Butcher
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- Oct 2004
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- Southern Highlands NSW
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- 1,898
How about just use calipers to measure and compare diameters of the spindle and backplate unthreaded sections?
But if you are sure there is clearance, that's OK.
Re-tap the backplate thread?
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6th Nov 2019, 07:23 PM #20
Hi Guys,
Running the correct tap through would help !
I don't like the suggestion that the thread is tapered. The face plate should screw on either way round.Best Regards:
Baron J.
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6th Nov 2019, 07:44 PM #21Diamond Member
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- Aug 2019
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- Revesby - Sydney Australia
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Tap? If I had one I would be tempted. I am actually machining up another large faceplate today, on my neighbour's lathe:
IMG_0297.jpg
so if I ever get that thread anywhere near acceptable, I will try refinishing the first bit of my little plate that won't thread on backwards.
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6th Nov 2019, 07:52 PM #22Most Valued Member
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- Jun 2007
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- sydney ( st marys )
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Generally before cutting the thread if that's what you are about to do , you would cut the recess/ undercut for the backplate as well as a 60 degree chamfer for the start of the thread first.
If you require a tap I may be able to supply.
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7th Nov 2019, 06:48 AM #23Diamond Member
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- Aug 2019
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Oops. I did forget to cut the register clearance first. Thread not finished yet (sooo many passes), so I'll tear that out before its too late.
...and, with cast iron, tear is the appropriate word and sound
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