1991 Mazak SQT-15M Help Needed

Good morning,

I am not super active on this forum and usually just read posts from time to time. However, I am making this post to see if I can get some help locating a Z-Axis home switch on our 1991 Mazak SQT-15M CNC lathe. We are trying to avoid having to pull a bunch of paneling and going on a wild goose chase for some random part that we aren't sure how to identify. Mazak has been helpful to some extent, but also aren't sure how to advise where we begin to look. The two gentlemen that we spoke to have limited knowledge of this machine. We are seeking all options in an attempt to avoid an approximate $2k service call for this. (We will if we have to, only as a last resort.)

We purchased this machine in May 2020. My husband is the machinist of our company and works on manual lathes and mills for all operations, but when it comes to CNC programming, we are a little out of our depth. We purchased this CNC, obviously used, from a 3rd party company. The machine was located out of state and we hired a trucking company to deliver. We were shown a video of the machine in operation prior to purchase, but have not gotten it programmed ourselves just yet. It is under power, but as I mentioned, we are new to CNC. However, we hired a CNC consultant to come teach us about the machine and how to program it. He kept running into a problem with the machine, was unfamiliar with this particular model and was unable to diagnose or locate the Z-Axis home switch with confidence.

When trying to home the Z-axis of the machine, the switch is not reading when it is pressed. The Z-axis keeps traveling until it runs out of travel and triggers an “overload” alarm. When attempting to home the X and Z-axis by activating the Home mode and traveling with jog controls the X-axis finds home and stops automatically there. The Z does not. He attempted to push what he believed was the switch in by hand while in the homing mode and it still didn't register, when he tried, he was not jogging the axis at all. Said that would be too dangerous.

We have been in touch with Mazak, but they have asked us to pull the part number off of the switch, recommending that we just order a part to replace it.

Does anyone have any insight into this machine and where we might find this Z-Axis home switch?

Any other insight would be welcome, as well!

Thank you in advance.

Usually, the Z axis hard limit switch is located at the rearward (tailstock) end of the machine and is accessible via sheetmetal covers on the back.
It usually looks "something" like a box with a little wheel on an arm and a wire coming out.

They stick over time from coolant/gook on them. They're not that expensive and easy to replace with hand tools. There may be a procedure Mazak has to do this.
If you remove the metal sheet metal cover on the back of the machine, you may be able to see it.

The oldest SQT we have has the switch mounted on the column and it moves with the Z axis. The plunger is pointed down and rides up onto the home dog. While standing at the back of the machine it will be about waist level, to just below. You can check continuity if you remove the cover and expose the wire connections. It should read OL on one position and 0.00 on the other (position meaning depressed vs not depressed). If you have the same reading in both positions replace switch. The switch is approx 1-3/4" x 1-1/4" x 3/4" and will have an electrical cable coming in from one end.

I would expect it to look something like the attached photo. All my machines take the same ones, which is why I have several new spares. IMO not worth cleaning them, every time I've cleaned one it never lasted more than a year or two before acting up again.

Hardplates said:

I would expect it to look something like the attached photo. All my machines take the same ones, which is why I have several new spares. IMO not worth cleaning them, every time I've cleaned one it never lasted more than a year or two before acting up again.

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Looks exactly like that on all of our SQT. Agree with not cleaning them, just not worth it.

chad883 said:

Looks exactly like that on all of our SQT. Agree with not cleaning them, just not worth it.

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Is this it? Also, while waiting on a call back from Mazak, would you happen to know if that number printed is the part number or should we keep looking?

Hardplates said:

I would expect it to look something like the attached photo. All my machines take the same ones, which is why I have several new spares. IMO not worth cleaning them, every time I've cleaned one it never lasted more than a year or two before acting up again.

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Thank you so much! Your photo was extremely helpful. I believe we found it, and definitely looks pretty sticky.

Do you source your parts from Mazak or have you found them better elsewhere? What do they usually run cost wise?

LadyBlueSteel said:

View attachment 311036

Is this it? Also, while waiting on a call back from Mazak, would you happen to know if that number printed is the part number or should we keep looking?

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That looks like it. You can try spraying some contact cleaner on it and working the plunger in and out. I would only do that to get by until the new one comes. Mazak will have it's own part number assigned to it. Should be in the parts book. I hav e not looked for them from another vendor, but I am sure they can be found.

LadyBlueSteel said:

Thank you so much! Your photo was extremely helpful. I believe we found it, and definitely looks pretty sticky.

Do you source your parts from Mazak or have you found them better elsewhere? What do they usually run cost wise?

View attachment 311037

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They are just standard Yamatake/Abzil SL1-A switches. I bought a bunch of them off ebay for under $20 each. They used to be made in Japan but I believe Abzil bought Yamatake or something like that and they are made in China now. I would rather new old stock that was made in Japan but I haven't had any issues with the Chinese ones.

When changing the switch be careful to note where the wires go as the switches can be wired for normally closed or normally open. They have 3 connection points but only 2 are used.

Before you go replacing that limit switch there is a proceedure (parameter change) to reset the home position, it is common for the machine to over-travel when 1st powered up after a move. I'll post what you need to do when I get back into work tomorrow morning.

gmc1724 said:

Before you go replacing that limit switch there is a proceedure (parameter change) to reset the home position, it is common for the machine to over-travel when 1st powered up after a move. I'll post what you need to do when I get back into work tomorrow morning.

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Thank you! I look forward to your response.

LadyBlueSteel said:

Thank you! I look forward to your response.

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Sorry I didn't get back to you yesterday, can you tell me what values you have in machine parameters A9 & A10 for your z-axis...