Brother TC-S2A Repair Question

Early in the year I picked up a used Brother TC-S2A-O. I have been slowly getting it setup and cleaned up. Not much got done this summer due to other projects. This week I took the way covers off and cleaned stuff up. The linear bearings look good and ball screws look good. The y axis ball screw moves about .03" axially when I pull the table back and forth in the y direction. The servo motor mounts to one end of a small cast iron box, the ball screw comes out the other end of the box. I took the cover off the box the coupler that attacheds the ball screw to the servomotor is in there. It appears that coolant got in there. I have not taken anything apart on the ball screw/motor assy. yet other than removing the cover from the box. I think there are a pair of angular contact bearings on the ball screw end of the box to keep the ball screw from moving axially. These may be bad and maybe the coupler is bad, I won't know until I get it apart. I called Yamazen and got a preliminary quote for some bearings. I also have a pdf doc from them that outlines change-out of many major components including the ballscrews. They don't seem to have a good detailed drawing of how all this goes together. One step they say to do is to use an indicator an find the location of the table with respect to the spindle in the y axis in this case and note it. Then during reassembly offset the axis in the control so it shows the same location. This is a little easier said than done since getting an indicator in the spindle, do all the work, and back into the spindle in the same location will not be so easy, at least with the indicators I have. Or do I need to bite the bullet and get the right indicator. Is it a coaxial indicator?

My question is how important is this step for me? Since I have no work offsets or any hard references in the machine yet does this matter? I understand that this is probably a question best asked of a Yamazen tech but it will be after Thanksgiving before I can call them again so I thought maybe someone here would have some insight.

When you reset the Y axis position, the center of the middle T slot will be the center of the Y axis stroke. It is not super critical. I usually just pick up a known position on the table if there is fixturing and a known work offset I can come back to. Basically for you, after you change out the Thrust Bearings inside the casting between the motor and ball screw, as long as your machine zero returns without alarming out that is all that matters. You can play with the grid shift parameter so that the center of the middle t slot is the center of the stroke. Not a big deal. when installing the new bearings watch out for the direction you put them in. They usually have arrows on them. Try to match the originals.

Thanks for the insight BrotherFrank! Something I don't understand though. I thought that a CNC machine had no idea where it's axis where on power up until it is zeroed each time, unless the machine has scales which mine does not. If my thinking was correct, which it appears not to be, none of this would matter since every time it gets powered up and zeroed it slowly heads toward the zero limit until it is hit. Based on what you and the brother manual are saying it appears that it does have some sort of permanent knowledge of its location.

Pete Deal said:

Thanks for the insight BrotherFrank! Something I don't understand though. I thought that a CNC machine had no idea where it's axis where on power up until it is zeroed each time, unless the machine has scales which mine does not. If my thinking was correct, which it appears not to be, none of this would matter since every time it gets powered up and zeroed it slowly heads toward the zero limit until it is hit. Based on what you and the brother manual are saying it appears that it does have some sort of permanent knowledge of its location.

Click to expand...

It does have known positions set in the machine parameters. So, to rule number 1, never change back up batteries with the power turned off the machine.

Pete Deal said:

I thought that a CNC machine had no idea where it's axis where on power up until it is zeroed each time, unless the machine has scales which mine does not.

Click to expand...

CNC machines can have absolute pulse coders and not have scales. They can also have scales and not be absolute. It depends on the MTB.

Newer machines use absolute encoders, which use batteries in the control box to always know where it is. But that started at S2C.

That makes sense then. I had no idea it had absolute encoders I thought they were just incremental. Thanks!

jid2 said:

Just so you understand your machine...

It has absolute encoders, which use batteries in the control box to always know where it is. So a Brother does not need to be homed on startup, which is nice.

Click to expand...

This is incorrect. The older machines use incremental encoders. They have to be homed at startup to know where it is. They switched to absolute with the s2c.

^^^ OK, listen to him he actually has a few of the older machines.

Well I ordered a blake coaxial indicator. I think this will be a little easier to get a repeatable before and after table location reading than my interapid indicator. But, I am back to not knowing why this would matter at all though if the machine does not know where its table is until zeroed.

Pete Deal said:

Well I ordered a blake coaxial indicator. I think this will be a little easier to get a repeatable before and after table location reading than my interapid indicator. But, I am back to not knowing why this would matter at all though if the machine does not know where its table is until zeroed.

Click to expand...

If you are unsure of what BrotherFrank posted than call Yamazen's service number in the morning.

Pete Deal said:

Well I ordered a blake coaxial indicator. I think this will be a little easier to get a repeatable before and after table location reading than my interapid indicator. But, I am back to not knowing why this would matter at all though if the machine does not know where its table is until zeroed.

Click to expand...

What is a coaxial going to do? An edge finder would be close enough for what you are doing since you dont have a plate or anything already on the table.

I never used one but it looks like it might be easier to get in and out of the collet chuck without moving things. Not used as a coaxial indicator just keep it in the one direction.

Pete Deal said:

I never used one but it looks like it might be easier to get in and out of the collet chuck without moving things. Not used as a coaxial indicator just keep it in the one direction.

Click to expand...

An edge finder will work just fine. It only really matters if you have a sub plate with critical locations already installed that you dont want to have to move.

Edge finder would work good. I over thought that one.

The older machines (A00 control and older) need to be zero returned at start-up. they have incremental encoders and need a reference point at start up. This is achieved with the two switches you see near the linear guides. One switch is the Origin switch, the other is the Over Travel switch. At start up the machine triggers the Origin switch and counts a certain # of pulses while the motor is slowly turning and where it stops is Machine Zero. This has a limited amount of adjustment which is the Grid Shift parameter. A simple way to get it running after working with the motor or ball screw, is to just zero return it. If it hits the Over Travel switch before it reaches Machine Zero, just loosen the coupling between the motor and ball screw and rotate it 90 degrees, tighten the coupling and try zero return again. This is the simplest procedure, Yamazen will be able to give you the full formal procedure when you contact them. Best Regards.

BROTHERFRANK said:

The older machines (A00 control and older) need to be zero returned at start-up. they have incremental encoders and need a reference point at start up. This is achieved with the two switches you see near the linear guides. One switch is the Origin switch, the other is the Over Travel switch. At start up the machine triggers the Origin switch and counts a certain # of pulses while the motor is slowly turning and where it stops is Machine Zero. This has a limited amount of adjustment which is the Grid Shift parameter. A simple way to get it running after working with the motor or ball screw, is to just zero return it. If it hits the Over Travel switch before it reaches Machine Zero, just loosen the coupling between the motor and ball screw and rotate it 90 degrees, tighten the coupling and try zero return again. This is the simplest procedure, Yamazen will be able to give you the full formal procedure when you contact them. Best Regards.

Click to expand...

Frank to the rescue!

jid2 said:

^^^ OK, listen to him he actually has a few of the older machines.

Click to expand...

oldies but goodies

Thanks all for sharing your insight. It will be about a week before i can get back to this.

You will be very happy with the s2a-0 once you get it up and running. For the money you spent that machine blows anything in that price range out of the water.