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Mensch-Machine
10-01-2010, 11:41 AM
The z-axis on my mill-drill (Smithy BX-288) does not decend smoothly. When I use the micro-feed, it mostly feeds smoothly, but at some points in the travel it hangs up and then *chunk* drops down.

Does anyone know a remedy to this problem?

Dr Stan
10-01-2010, 11:46 AM
Sounds like you have a tooth or teeth missing from the gear or the rack. You'll need to disassemble it to diagnose the problem.

dp
10-01-2010, 11:48 AM
Are you talking about the column or the spindle?

Mensch-Machine
10-01-2010, 12:18 PM
Are you talking about the column or the spindle?

Spindle. No problems moving the head.

bruto
10-01-2010, 12:54 PM
Does it go up smoothly? If so, I doubt it's bad teeth. If it's clunking going down, I'd suspect that there's a little binding that prevents the spindle from dropping by gravity, and combined with lost motion in the gears, it will stop, then drop. I don't know what you can do about that except to make sure it's well lubed and the clamp is not tightened partway.

Jim2
10-01-2010, 01:29 PM
I've got a square-column mill that does this too. I just tighten down the quill clamp so that it binds enough to hold back against the force of gravity. Then I take up the backlash in the micro-feed and feed it down. I've got a DRO on the z-axis, so it's easy to keep track of how far it's moving, etc.

Jim

QSIMDO
10-01-2010, 05:02 PM
There are 2 or 3 bolts that hold the micro-feed and lever feed assembly to the head if it's at all like my Industrial Hobbies machine.

I had to loosen and rotate that assembly to a point where the micro-feed functioned correctly.

(That micro-feed is definitely on my project list for improvement.)

Your lever feed works correctly?
Return spring installed ok?

M.I. Twice
10-01-2010, 07:24 PM
The z-axis on my mill-drill (Smithy BX-288) does not decend smoothly. When I use the micro-feed, it mostly feeds smoothly, but at some points in the travel it hangs up and then *chunk* drops down.

Does anyone know a remedy to this problem?
I had this problem with my baby bee mill. In one of the English mag. they had a fix, they used a shiv, a small cable and a spring. This takes up the lost movement. e-mail me for a pic.
M.I. Twice

bradfordking
10-02-2010, 04:37 PM
I agree with Jim2 you have to put a little drag on the quill. That goes as general for all machines, mills, lathes, if it travels too easy its going to be sloppy. BK

Black_Moons
10-02-2010, 04:38 PM
the weight of the quill should force it down..

Tryed putting some way oil on the quill?

lazlo
10-02-2010, 04:46 PM
The mill/drills all do this -- there's a lot of slop in the rack and pinion gear that drives the quill. There have been a bunch of articles posted on it -- so folks have made eccentric cams to change the center distance between the fine-feed pinion and the rack cut into the quill.

It's seriously aggravating when you have the quill set for a specific Z-height and you loosen the quill clamp to move and the whole quill drops about a 1/16"...

chiphead42
10-02-2010, 05:55 PM
M-M I solved this problem with a small cable small pullys & lead weight.
I used 1/16 ss cable, do ot use he plastic coated. 3 or 4 small ballbearing pulleys from window hardware. Approx. 25# lead. I used pcs. of 1x1x1/16 angle cut & shaped to wedge between the head casting & sheet metal guard at top. Attach end of cable at top behind the quill. Around 1 pully in the clamp slot at the rear of the peice at the bottom of the quill. Up over another pulley at top back toward the collum. Route cable out between casting & sheetmetat guard. Over 1 or more pulleys & attach to lead weight. Allow for about 6" vert travel. I poured my lead into a large can with an Ibolt. This will always hold the quill back against the rack preventing the sudden unexpected drop. Hope this helps chiphead42

Doc Nickel
10-02-2010, 07:22 PM
My old Jet M/D had springs built in, to pull the quill up- like a spring return for a drill press, except these were plain extension springs, not the watchspring seen in most small drills.

That way, when the fine feed was in use, the springs tensioned the spindle against the gearing to take up the 'slack'.

Wasn't particularly elegant, and there was indeed a lot of slack to take up, but it worked.

Doc.