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Bantam feed not working

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Allen Moore 114/02/2020 23:15:37
6 forum posts

Hi guys

Hoping one of you knowledgeable chaps maybe able to help me. I am still learning to use my lathe and think I may have damaged it. I was doing a cut with the feed and set the stops on the carriage to stop at same place. The idea being to stop the feed just before the stop then hand wind to the stop. Unfortunately I couldn’t disengage the feed before it hit the stop so I hit the e button. I could disengage the feed lever as it was tight against the stop. I managed to wind the stop in and disengage the feed.

Since this happened the feed does not work. I have taken the end cover of the drive end and the cogs are all driving(itruns when the cover is removed). I have read that there is a shear pin but I think that hasn’t sheared and it’s something in the bottom gear box. Pics below if any help. The pic of the drive end was taken when the lathe was running and all cogs were turning but the feed screw wasn’t. I hope I haven’t damaged it beyond repair.

cheers in advance

upload_2020-2-12_18-46-19.jpeg

upload_2020-2-12_18-44-44.jpeg

Steviegtr15/02/2020 00:33:10
avatar
458 forum posts
121 photos

I do not know your model of lathe. Can you do a sort of logical assessment starting at the beginning, the drive & slowly follow the drive to a point where it stops. It is only gears going round. So at some point they stop going round & that is where the problem is. Sorry I cannot be of more help & I am sure someone will be along that knows your model & can be of more help. Certainly looks like a nice machine you have

Steve.

not done it yet15/02/2020 08:24:48
3911 forum posts
15 photos

You have learned that it is never a good idea to use a solid stop when under power feed! Either Always allow more than sufficient space to stop with the e-button, or preferably a moveable indicator rather than a solid stop. Check as above - you will either have broken a safety pin or a gear (hopefully only one, if it has), I expect.

It is still possible that only the shear pin has broken. Good luck as you check through the drive.

DC31k15/02/2020 08:37:18
84 forum posts

As Steve says, attack this logically. It is just a machine.

Do you have a manual for it? If not, please obtain one as all Colchester manuals have full exploded diagrams of the entire machine. This will tell you how the spindle links to the feed mechanism and where the shear pin may be.

If you find a manual online, please post a link so we can all look at it.

When you were cutting, were you using the leadscrew and halfnut (lever at headstock end of apron)? Or the sliding feed (lever on face of apron below cross-slide hand wheel)? The sliding feed should disengage automatically when hitting the stop. The leadscrew will not.

The sliding feed disengagement is all in the apron so it may need cleaning and lubricating.

Any shear pin will be in a place semi-easily accessible and not buried inside the gearbox.

The gears may be rotating but often one of them is on a carrier that is (shear) pinned to its shaft.

Put a pair of soft-jaw pliers on the feed shaft near the tailstockand turn it gently. The output of the gearbox where the leadscrew dog-disengagement should also turn. The output shaft of the gearbox where the change wheel is should also turn. If the SHAFT turns but not the gear, that is where the shear pin is.

Emgee15/02/2020 09:08:08
1343 forum posts
212 photos

Allen

Remove the small gear immediately below the spindle in your picture, there is a shear pin fitted at this point which fails with excessive load.

You may need to check the apron engagement lever mechanism because that should release the feed when resistance to travel is felt.
There are bed and crosslide adjustable stops available which rely on the automatic disengagement of the drive so clearly it's OK to allow the stop to disconnect automatically.

Another point is the end cover guard safety limit switch has been disabled from the electrical circuit or you wouldn't be able to run the motor unless holding the switch closed, I would advise the switch is re-instated to provide some measure of safety as intended by Colchester.

Emgee

switch note added

Edited By Emgee on 15/02/2020 09:13:23

DC31k15/02/2020 10:23:39
84 forum posts
Posted by not done it yet on 15/02/2020 08:24:48:

You have learned that it is never a good idea to use a solid stop when under power feed!

That statement is not universally true. The Bantam (and Chipmaster) have a very clever mechanism that allows precisely this. If the manufacturer of the machine has given you this facility, why not use it?

not done it yet15/02/2020 11:54:48
3911 forum posts
15 photos
Posted by DC31k on 15/02/2020 10:23:39:
Posted by not done it yet on 15/02/2020 08:24:48:

You have learned that it is never a good idea to use a solid stop when under power feed!

That statement is not universally true. The Bantam (and Chipmaster) have a very clever mechanism that allows precisely this. If the manufacturer of the machine has given you this facility, why not use it?

If it worked to automatically stop, fair enough. I use my auto long travel trip at every opportunity. A delightful improvement over the earlier models of my marque. Used to cut to a shoulder, or to trip before striking the chuck. It is easily checked when setting the trip point.

Howard Lewis15/02/2020 12:21:51
2699 forum posts
2 photos

Wearing a clever dick hat, just before the sold stop, I disengage the power feed, and feed the last bit (0.025 - 050" ) by hand, up to the stop.

Hopefully, the problem is just a shear pin which has done its job and protected the rest of the drive train..

Even a brass key would served this purpose.

Howard

Macolm15/02/2020 21:54:57
1 forum posts

Allen,

The problem is obviously not the usual shear pin since the quadrant gear train still rotates up to the gearbox input. Firstly, best not run the machine under power anymore, since this could cause more damage if there are teeth off gears. However, looking at my moth-eaten parts list, there is a pin as the output coupling to the power feed shaft (this assumes you were not using the lead screw when the incident happened). It is not clear if it is designed as a shear pin. If you disconnect the power feed shaft (it has a slot driven by the pin), it should be possible to check it. Undo the RH bearing block and slide shaft and lead screw assembly to the right (no need to remove completely).

You do not report any gearbox noises, so it is hopeful that damage may be (relatively) minor. Unfortunately, it looks like you need to fully dismantle the gearbox to fix. There is also an oldham type coupling for some of the gears, failure of which would prevent those particular gears from working. Start by disconnecting the quadrant train to the gearbox, then turn input by hand, trying all gears. The gearbox can be removed for easier dismantling. Reassembly is a fiddle to get the selectors correctly engaged.

You are a bit unlucky to have this problem. The end stop release works reliably on my Bantam. However, I recall an article in MEW years ago where the author had trouble with the release. I do not remember the details, but the calibration of the springs that control the release force was incorrect. Perhaps someone can point you to checking if this could be the problem.

F

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