Powermatic model 90 lathe Micro switch

[Bruce Koch]

I have a 1980 model 90 lathe 3 phase. How do you rewire the unit if you eliminate the micro switch in the head. It has furnas control. There is a red, blue and black wires going to the switch. I,m lost. The switch is broke and I think it can be rewired to make it work. Any help?

[M Toupin]

The micro switch is a safety device so the lathe will only start with the speed set at the lowest setting, but you probably already know that. Finding a suitable replacement shouldn't be too difficult, but if you're comfortable bypassing the switch, go for it. It's just wired in parallel with the start (NO-normally open) and the stop (NC-normally closed) switches in control station on the front of the lathe. Pull the switch out and unhook the wires from the start & stop buttons. Wire the start & stop buttons together using the terminals the switch wires were connected to. Here's the manual http://vintagemachinery.org/pubs/detail.aspx?id=2783 Page 15 covers the switch & wiring.

Mike

[M Toupin]

Should have mentioned, the wires are actually all terminated inside the starter box, here's a pic. The micro switch wires are tied into the start/stop with the wire nuts.
207986
Mike

[Bruce Koch]

I connected the two wires together and I hit the start button it runs fine but when I release the button it stops. What do I do now?

[M Toupin]

Just realized the link to the manual was wrong, here's the correct link http://vintagemachinery.org/pubs/detail.aspx?id=822 Page 15 covers the switch & wiring. Just so I understand correctly, you've switched out the 3ph motor with a new 1ph motor and you want to eliminate the micro switch correct?

Mike

[Dave Lash]

The reason the lathe dosn't keep running when the start button is released is that the holding contacts on the starter are not connected. The manual shows the micro switch drawn as a single pole double throw switch, with power to the starter going through both the normally open and the normally closed contacts, which would not work. The description of the circuit states that the switch is a "two pole two stage unit" meaning that at some point of switch travel both sets of contacts will be closed at the same time. To bypass the switch the three wires from the switch must be connected together to allow the holding contacts to operate; but as the manufacture included a switch to insure that the lathe could only be started in the slow speed, they must have felt that there was a chance of damage by starting at a high speed. The best solution would be to replace the switch with the same part number (BZ2GW822) to avoide the chance of damaging the lathe. A quick Google search of the part number shows several vendors with varing prices, but onlinecomponents.com shows the price as $17.12 and has a link to the manufacture data sheet showing the sequenc of operation of the switch.
http://www.onlinecomponents.com/honeywell_bz-2gw822.html?p=11929072

[Bruce Koch]

I've been gone for a few days. It now works. Thanks guys