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Mopar_Mudder
03-30-2019, 05:08 PM
I am looking at used mills and wondering how much backlash on the X and Y would be considered normal. One I am looking at is said to have 10 to 20 thousands.

danlb
03-30-2019, 05:16 PM
That is within the normal amount. Normal procedure is to avoid climb milling and always take out the backlash (wind the table out and then in every time) before each cut. You need to do that when you have .002 backlash or .050.

More important than backlash is wear. Backlash CAN BE an indicator of wear, but that wear is often in the nut and not the lead screw. Make note of the backlash in the middle, then again with the table moved left and right. The difference should be leadscrew wear.

brian Rupnow
03-30-2019, 05:17 PM
Backlash is something we all just learn to live with. If the machine is equipped with digital readouts, you never think much about backlash. If you don't have digital read outs, then you always have to be aware of the last time you moved something were you turning the dial clockwise or counterclockwise.

old mart
03-30-2019, 05:28 PM
The museum's drill mill is a pain to use trying to remember which way you were last turning the dials, as Brian mentions. I put one of the cheap dro's on the quill and that is great, but I cannot afford the dro's for the X and Y. Digital readouts are one of the best investments for a mill.
There may well be adjustments to reduce the backlash, either the nut and/or the leadscrew. That much you are expecting wouldn't put me off.

Mopar_Mudder
03-30-2019, 06:17 PM
Thanks for the info. It does have DRO on it so I think I will make him an offer.

Mcgyver
03-30-2019, 06:21 PM
what Dan said. Just about the only reason to pay attention to backlash is as an indicator of wear...and 10 -20 thou is very little wear (there has to some clearance or the screw wouldn't turn)

Erstwhile
03-30-2019, 06:36 PM
I am looking at used mills and wondering how much backlash on the X and Y would be considered normal. One I am looking at is said to have 10 to 20 thousands.Alot lol, get a dro and dont look back.

Sent from my SM-G960U using Tapatalk

J Tiers
03-30-2019, 06:45 PM
You might check, if you get the mill, whether any of the backlash is due to either the feedscrew moving, or the nut moving.

From time to time I see someone quoting an amount of backlash that would indicate the threads were entirely worn off the screw and nut. The facts generally are that the feedscrew or the nut is moving so that either tightening screws or adjustment of thrust bearings brings the backlash into the normal range.

Rich Carlstedt
03-30-2019, 07:30 PM
Reading the posts , it time for a tip to manual mill operators and backlash control.
When I supervised a die shop, I taught this method to my mill hands.
For X axis only, lock the the table with the clamp.
On the right side of the mill ( as you look at it) turn the handle clockwise till it stops and set the dial to 0
On the left side of the mill, turn the handle (also) clockwise and zero the dial. Then un-clamp
Now when you want the table to move to the left, you turn the right handle Clockwise and the dial matches the move
To move to the right, You only use the left handle and turn it clockwise and the dial matches the move

So you only turn clockwise and the backlash is "Pre-compensated" by you setting the dials ahead of time and it eliminates
remembering which way to turn a handle and make it a habit
Rich

old mart
03-31-2019, 08:49 AM
Good tip, I will have to practice it a bit, the mill drill only has a scale at the right hand end of the X axis. I may make a scale for the other end, it's not difficult.

MattiJ
03-31-2019, 12:40 PM
Close to half turn is too much

larry_g
03-31-2019, 12:59 PM
On these threads about backlash it seem that most focus on the screw/nut thread wear. But there is a third place that will introduce backlash and that is the thrust bearing at one or both ends of the leadscrew. Any clearance in the thrust bearing will show up as backlash. Mount an indicator on the table, carriage, cross slide, or whatever and probe the end of the leadscrew. Push/pull the table and you will indicate the clearance in the thrust bearing.

lg
no neat sig line

J Tiers
03-31-2019, 03:12 PM
Or the nut being loose (post 8)

Doc Nickel
03-31-2019, 03:44 PM
My first mill drill eventually had about a third of a turn on the X handwheel of backlash. I didn't know any better, figured it was wear, learned to live with it.

When I went to rebuild it years later, I discovered the nut was loose at the right-hand-end handwheel bearing. Snug that back up and all of a sudden it was back down to just 10-12 thou of slop.

Then again, when I got my Exacto, the X-axis leadscrew nuts could be slid off the screw. :D (Mechanical damage in that case, not wear- the screw was nearly perfect.)

Doc.

projectnut
03-31-2019, 04:43 PM
As a point of reference a Bridgeport Series I machine comes from the factory with .003" to .005" backlash on both the X and Y axies.

Sparky_NY
03-31-2019, 05:59 PM
As a point of reference a Bridgeport Series I machine comes from the factory with .003" to .005" backlash on both the X and Y axies.

+1 And the BP maintenance manuals call for setting it at .005 (those with split adjustable nuts)