How much backlash is needed or just plain unwanted???

Happy Thanksgiving!

I have reassembled the saddle on my mill. I took the two nut system out, cleaned everything, and put it back together. Following the instructions, I adjusted the nuts to eliminate some backlash in the y-axis mechanism. Currently, it is at .003" of backlash for the saddle movement as measured with an indicator. What is the best practice when it comes to adjusting out backlash? Should one leave a bit of backlash to reduced some wear on the nut and screw? Should one always try for zero backlash?

I understand that backlash can be dealt with while using the machine. My question pertains to setting up the machine after having removed and cleaned the parts.

Thank you!

Andy

Guncraft said:

Happy Thanksgiving!

I have reassembled the saddle on my mill. I took the two nut system out, cleaned everything, and put it back together. Following the instructions, I adjusted the nuts to eliminate some backlash in the y-axis mechanism. Currently, it is at .003" of backlash for the saddle movement as measured with an indicator. What is the best practice when it comes to adjusting out backlash? Should one leave a bit of backlash to reduced some wear on the nut and screw? Should one always try for zero backlash?

I understand that backlash can be dealt with while using the machine. My question pertains to setting up the machine after having removed and cleaned the parts.

Thank you!

Andy

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screw usually worn more at center of travel. i would go as tight as practically possible check the full range of screw travel. often this means more backlash at center of travel and less backlash at extremes of travel

There will always be backlash. Do not expect the screw and nut to hold the axis on location. The gib does that along with the clamp. Do not climb cut with a Bridgeport, unless ballscrews are installed.
New Bridgeport backlash ~0.002 to 0.007
Used, cleaned, and adjusted ~0.007 to 0.015
The backlash could be 0.050 and it won't matter.
Tight settings accelerate wear of the nut.
Set the backlash for the sweet spot. Open it up when moving for longer travel.
There is a limit. Know when the adjuster bottoms out. Otherwise the knuckle casting that holds the axis nuts will crack at the adjuster location.
John

John,

I realize wear is a factor of machine use, but how much more accelerated can I expect the wear to be between a .003" backlash setting and a .007" other than "twice as quickly"?

Thank you!

Andy

Guncraft said:

John,

I realize wear is a factor of machine use, but how much more accelerated can I expect the wear to be between a .003" backlash setting and a .007" other than "twice as quickly"?

Thank you!

Andy

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does screw turn hard or normal pressure to turn it ?? as long as it turns easy along full screw length it is not too tight

It turns very easy.

Andy

Good, It's adjusted correctly!

.003 or .030, if a manual machine, you have to take it up. No biggy!

Guncraft said:

John,

I realize wear is a factor of machine use, but how much more accelerated can I expect the wear to be between a .003" backlash setting and a .007" other than "twice as quickly"?

Thank you!

Andy

Click to expand...

Andy,

This is how to check regardless of the setting.
Start with clean screw and nut.
Apply the lube. Use the machine over some time period.
Use a clean white wipe and inspect for the presence of bronze washed into the oil.

For instance:
If the nut is adjusted for low backlash in the center of travel and the table is moved to the full extent of travel the guarantee is that bronze will be wiped from the thread profile.

The best setting is that which leaves no trace of bronze in the oil.

To check the saddle screw. Park the table in the typical center of travel. Back off the four cap screws.
Pull the saddle towards the operator to the full extent of travel. The screw is extended out of the cavity and is easy to check.

This is a good time to set up a pair of indicators some distance apart touching the saddle. Have the saddle in the center of travel. Indicators may be on the ways or on the sides of the saddle. Try to rotate the
the table cw-ccw and watch the indicators. A wide variance may show a loose gib, bottomed gib, or high degree of wear.

The machine has split nuts in the saddle per post #1. The flank of the thread of only one of the nuts is working during travel towards the column. The flank of the other nut is working as the saddle moves toward the operator. Each half of the nut is working/wearing twice as hard/fast as a new nut that was not split. A tight setting will accelerate wear.

John

they make double nut with spring loading so lead screw is always in contact with zero backlash normally. if cutting pressure is greater the anti backlash spring setting then you will get backlash when spring deflects at high pressure levels. obviously the tighter the spring setting the faster the wear and harder to turn screw
.
anti backlash spring to prevent the loose rattling of extreme backlash when slide is loose

jhruska said:

Do not climb cut with a Bridgeport,

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You can climb cut on a Bridgeport if you know what your doing, with or without ball leadscrews.

I went ahead and adjusted it out to .005" to avoid some unnecessary wear. I do have a DRO which should help me see the backlash and account for it.

Thank you!

Andy

Guncraft said:

I went ahead and adjusted it out to .005" to avoid some unnecessary wear. I do have a DRO which should help me see the backlash and account for it.

Thank you!

Andy

Click to expand...

.005 is excellent for backlash.

I was under the belief that with a DRO, backlash would become irrelevant since the DRO is measuring absolute table travel in X or Y directions.

My big Webb Mill has ball screws with zero backlash in Y and .007 in X. It hasn't changed at all in the 5 years since I got the machine. I haven't worried about backlash since I installed a 2 axis Mitutoyo DRO. Maybe I should?

Newman109 said:

.005 is excellent for backlash.

I was under the belief that with a DRO, backlash would become irrelevant since the DRO is measuring absolute table travel in X or Y directions.

My big Webb Mill has ball screws with zero backlash in Y and .007 in X. It hasn't changed at all in the 5 years since I got the machine. I haven't worried about backlash since I installed a 2 axis Mitutoyo DRO. Maybe I should?

Click to expand...

I have Mitutoyo DROs (KA counter and AT-715 scales) on both of my mills, and find them to be accurate and durable, as long as I have done a test of positioning and set the error compensation as required.

I think generally that a DRO will make it unnecessary to worry about backlash on a single axis, but on a machine that is well-worn, the DRO cannot account for errors related to drift between axes due to wear, when repositioning using more than one axis. This is essentially lost motion. I would be more concerned about your comment stating .007 in backlash on a ballscrew-equipped machine. That sounds pretty serious for a ballscrew.

specfab said:

I have Mitutoyo DROs (KA counter and AT-715 scales) on both of my mills, and find them to be accurate and durable, as long as I have done a test of positioning and set the error compensation as required.

I think generally that a DRO will make it unnecessary to worry about backlash on a single axis, but on a machine that is well-worn, the DRO cannot account for errors related to drift between axes due to wear, when repositioning using more than one axis. This is essentially lost motion. I would be more concerned about your comment stating .007 in backlash on a ballscrew-equipped machine. That sounds pretty serious for a ballscrew.

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The .007 backlash is partially due to end play between the supporting ball bearings on the carriers on each end of the table. Since the machine is from 1987 and is a manual machine, the alternative if the backlash is not cured with shims would be replacement or rebuild. That would be a lt of money for .007 on a manual machine. I haven't felt like fooling with it since I installed the DRO.

Try not to be so concerned. It will be alright.

I know the feeling. ;-)

I don't worry about backlash. I've got a DRO.
JR

You need only enough clearance to keep from going metal to metal . Most machines never get any wear at the extremes of travel . Therefor that is were you need to check back lash ad live with the wear induce back lash.