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10th Nov 2021, 01:20 PM #1New Member
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Hercus model ARM lead screw spinning too fast.
Hi All,
I'm just a hobbyist enjoying my old Hercus model A. I have made all sorts of bits and pieces for my motorcycles, including cutting imperial threads.
My son has a Hercus model ARM and with the gearbox set to the slowest lead screw setting, the lead screw is spinning too fast.
We tried to cut a thread the other day with a 1mm pitch and using the correct positions on the two gear box selectors and with the chuck driven by the back gears, the thread ended up with a pitch of a little over 5mm.
We seem to have some incorrect gears? Any help would be appreciated.
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10th Nov 2021, 03:39 PM #2Most Valued Member
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What gears have you got set on the stud banjo and screw at present?
What spare gears do you have?
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10th Nov 2021, 05:37 PM #3New Member
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Thanks for responding pipeclay.
The stud gear has a 24 running on the tumbler gears and a 45 outside that running on the idler gear which is then running on a 20 on the banjo? with a spare 50 outside that.
Sorry - not sure which is the banjo gear and which is the screw gear.
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10th Nov 2021, 06:03 PM #4New Member
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Hello again pipeclay.
Your response has prompted me to find the solution I think.
The 45 should be down on the banjo? running on the idler gear.
The 20 should be on the stud gear.
The 50 is the spare stud gear and should be stored on the outside of the banjo.
Does that sound correct?
I have let my son know and he is going to try that.
Thanks again for your help.
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10th Nov 2021, 06:31 PM #5Most Valued Member
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The thread chart on the box will show the correct position for the gears depending on fine or coarse thread.
The gear on the outside of the reverse tumblers is the Stud the gear on the Banjo bracket is the Idler and the gear on the outside ( left of gearbox from standing in front facing headstock ) is the Screw.
On the Screw there should be 2 gears or a gear and spacer, this takes up the additional shafting on the screw shaft.
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11th Nov 2021, 08:16 AM #6Senior Member
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What you have there is correct, unfortunately Hercus did not put the screw gear teeth number on the gearbox plate on the 9" models yet on the 260 they did.
here is a link to the standard gear configurations for the lathe models.
Standard gear configuration for Hercus 9" and 260 lathes
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11th Nov 2021, 09:46 PM #7New Member
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Thanks Everyone.
Thanks heaps tinkerer77 and pipeclay- my sons Hercus model ARM is functioning correctly now and as a bonus, you have directed me to information that will allow me to cut a metric thread on a flywheel puller for my old Montesa Cota 348 using my imperial model A.
I'm loving this forum.
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12th Nov 2021, 10:15 AM #8Senior Member
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There's plenty of people on the forum that are always willing to help out, it's all a bit confusing when you are starting out, not sure if you found this but I put this together a little while back to help explain compound gears
https://metalworkforums.com/f189/t20...9-model-lathes
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14th Nov 2021, 09:47 AM #9New Member
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