Stories from the Wall: Hyd-Mech PLC100 - a 35 Year Mystery Solved

The Hyd-Mech PLC100 was a long sought after “trophy” for my wall. I had been looking for one for my trophy wall for years, checking back with a longtime contact (Jim), every year or two.

I have frequently come across PLC100’s while visiting different client factories, and it is tremendously gratifying to see them in still action, doing what they were designed to do, nearly 40 years ago. They don’t break down and the operators love them, so they’re never pulled out of service.

A couple months ago, Jim retired. He called me up on his second last day and told me that while cleaning out his office, he came across a PLC100 in the bottom of a closet. I was thrilled and drove to see him immediately.

In the early years, Jim and I spent a lot of time visiting customers together. We relived a few of the most challenging adventures. One was in Rochester, and another was in Wisconsin. They both wanted cutting accuracy that seemed nearly impossible for a band saw to achieve, but we aimed to please, so with dogged (sometimes irrational) determination, we pursued their utopic objectives.   

We didn’t quite get there, but we came awfully close. The pursuit of their near utopic objective of plus or minus 5 thousands of an inch accuracy (when the variation due to blade wear could be greater than that) drove us to refine and improve to the point we could easily exceed what 99% of the customers needed, and in the end, even these two most challenging customers accepted that we had given it our very best effort and settled for what we did achieve. We could only get to plus or minus 7 or 8, and at that point, we were really splitting hairs.

As Jim and I were reliving some of those early career shaping adventures, I noted one of the first challenges of the design was the fact Hyd-Mech wanted to keep using AC solenoids on the hydraulic valves. All the manual versions of all their saw models used 115 VAC switches and solenoids, and for inventory and cost reasons, they didn’t want the new automatic models to have to use 24 VDC coils and controls, which would’ve been far easier for me.

The first automatic control prototypes proved to be problematic. They used triac outputs which frequently had blown open. When I replaced the triac outputs with relay outputs in a subsequent prototype design, they frequently fused closed. We built about 30 of the first two versions, and from those lessons learned the hard way, we refined the design into what became the standard, PLC100 version, that still runs in many factories today.

The key development was the incorporation of a zero-cross detection circuit that latched or unlatched the relays only at zero-cross, eliminating the fused relay contact problem. It was a clever design element that was the difference between success and failure, and it ended up being something we incorporated into many other critical products where AC voltage had to be switched on and off to inductive loads. It was very valuable “knowhow” for my company then.

As I was re-living this now forgotten key design breakthrough, I started to talk through the math of the utopic objective pursuit mentioned earlier (plus or minus 5 thousandths of an inch). Zero-cross occurs every 8.3 milli-seconds. At slow shuttle travel speeds, the shuttle moved just less than an inch a second, meaning it could travel about 6 or 7 thousandths of an inch in 8.3 milli-seconds. It would be impossible to achieve any tighter tolerance than we did, without switching the entire control system and solenoid coils to 24 VDC, or reducing the slow speed travel rate to half an inch a second. It was an “Aha!” moment, 35 years in the making. We determined for certain that we had achieved the absolute optimal result possible.

There were many, many lessons learned from the development of the PLC100, and many memorable adventures and times spent with many great people. The early days spent with the founder, and his family members that worked there, and the young entrepreneurial leaders that built their distribution network, were amazing. I could write pages about what I learned from them and what I experienced with them – not just about saws and manufacturing, but about life as well.

But for this piece, I’ll keep it to just my trophy on the wall – the PLC100. Some lessons took 35 years before I figured them out, but others benefited the company nearly immediately, and for four decades to follow.

The PLC100 was the first product I designed where the company didn’t charge the customer for the design service. We did all the design work for free and owned the finished design, firmware and intellectual property as a result.

It was a risk, but in those days, we didn’t have much to lose (and not much else to do), making risks like that easy to take.

I think we sold between 500 and 800 units over 8 years – not an astounding number, but a big enough number to affirm the decision we made, and it encouraged us to look for other opportunities to do the same thing.

And those opportunities came – the most significant one directly as a result of someone seeing one of the first PLC100s in action.

A Vice President of R&D for a small, up and coming local water disinfection company was looking to purchase a bandsaw for their shop and he was impressed by the easy, intuitive function of the controller. He didn’t buy a saw that day, but he took note of the logo on the bottom of the controller and gave me a call shortly afterwards.

That turned out exceptionally well for the company, but that will be another Story from the wall.

Stay tuned.