G4003G able to stop carriage threading feed with minimal pressure

keeena

keeena

H-M Supporter - Gold Member
H-M Supporter Gold Member
Joined
Jun 10, 2019
Messages
534
I just bought a lightly used G4003G lathe and had a question about behavior of the leadscrew. When I was in the lowest TPI setting (4TPI, tumbler in A-1) I was able to easily stop the carriage by putting minor pressure on the hand wheel. This caused a bit of a grinding noise. The noise would stop and carriage continued once pressure was released. I was able to do this twice when I was testing the lathe before I bought it. I haven't had a chance to look more closely yet (just bought/moved 2 days ago, haven't powered up here). Tumbler and change gears look perfectly OK.

I'm pretty sure the lead screw stopped during this test so it wasn't a half-nut engagement problem. I'm pretty sure this model doesn't have a clutch. I also was not able to produce this at higher/high TPI, which seems to make sense because the higher TPI gearing would mean I'd have less leverage over the gearbox. But this could have been a fluke... When working the lathe by hand, I did notice that its possible to get the leadscrew/feed rod selector in a near-neutral position but still have a slight engagement on the leadscrew gear. This is the only thing I can thing of that might have caused the issue...possibly not fully engaged and I was just able to slip/grind gears because they were barely meshed.

Anyway - just hunting for ideas before I have a chance to hook it up and play. :)
 
If the leadscrew did indeed stop then either there is a friction clutch somewhere or a shear pin that has sheared. The very coarse threads like 4 tpi put a lot of stress on the geartrain so you don't want to put undue resistance on the carriage under those conditions, make sure everything is moving smoothly
Mark
 
Check your gear change knobs and make sure they are properly engaged.
Test again
 
Belts slipping? Out of adjustment?
I don't know this lathe, just fishing.
 
You G4000G probably has a ball detent clutch on the leadscrew. I have an older Griz 12x24 and "discovered" it by accident one day. You can adjust the tension behind the balls to set the release torque. See thread:
www.hobby-machinist.com

Question About Ball Detent Clutch Adjust On A Jet Gh-1340a Lathe

My unplanned project lathe came with a ball detent clutch that was not mentioned or shown in the manual. I have looked at a number of Jet Lathe manuals and have not found one that provides definitive information for this type clutch adjustment. The newer model Jet lathe uses a slip clutch but...
www.hobby-machinist.com www.hobby-machinist.com
 
markba - No clutch and did not shear the pin. I was only putting very light pressure on the hand wheel nothing that would come close (I would think) to popping a roll pin / shear gears / etc... Or is light pressure still enough to create a problem at low TPI?

hman - I looked but no dice; definitely no clutch on this one. Like Mitch said: just a roll pin.

The more I think about it, I'm thinking/hoping the leadscrew selector gear was barely engaged. Still in the process of cleaning the the lathe so haven't had a chance to re-test.
 
If your lathe is powered off and you engage the half-nuts, you will probably have some chuck back and forth with the longitudinal hand wheel which is looseness/wear in the half nuts. But you should be able to pull pretty hard on the hand wheel once the slop is taken out without anything moving.

You shouldn't see the lead screw itself chucking back and forth with hand wheel movement with the half-nuts engaged. I had that condition on my Clausing 5418 lathe and had to make an adjustment in the gear box.

Bruce
 
Confirmed...user error. The Feed / Lead Screw selector must not have been fully engaged when I initially was looking at the machine.

Really looking forward to using this! Coming from the G9972z: it's a big step up.
 
Have my G4003G for 6 years. Luv it! I read you solved your problem. Good! For info, there's no clutches on that machine but the lead screw and feed rod are locked to the QCGB by a roll pin that may or may not shear. I recently did a dumass and bent a shaft in the apron. The pin held. When you're not using the crossfeed don't leave it cranked all the way towards you and bottomed out against the hand wheel boss. If you want long feed and accidentally engage the cross feed you could break something if the cross feed can't move.
 
You must log in or register to reply here.
Back
Top