MachTach Build

I built 2 of them and have a third for backup. Very well engineered kit and a really great guy who designed and sells them. I used a magnetic pickup with six magnets on the mini mill and a gear tooth pickup on the mini lathe. They work great.

Roy
 
mksj said:
Built a few of the MachTachs, although I prefer to mount them in Hammond diecast enclosures. Not as easy to do vs. the 3D case. I use the SFM on larger diameter work on my lathe, helpful to tell you if you are ball park SFM. Most recent version does metric. More recently I have also been adding a precision 3 turn speed pot in my tach enclosures. Much better quality pot and I do not need to take up a larger 22mm hole. One minor issue I have had with the MachTachs is they require a 9V power source, typically most low voltage control systems are 12 or 24VDC. Some systems I needed yet another step down converter or add a heat sink to the regulator if there is room (you can see below that the heat sink needed to be modified to fit the case). I also used a more standard round threaded hall sensor on lathes if you have the room. In one case the tach was sensitive to VFD electrical noise, but I managed to work that one out. The documentation in the manual is very clear, also availability of different sensors makes this tach a bit more adaptable. Had a recent discussion with the builder and some suggestions, nice person and listens to comments.

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Mark,
What does the additional 3 turn precision POT you add do?

How are you typically providing 9V for power? Do you think the gent who sells the package would consider an option for 12VDC power?
 
Blackjack thanks.

A little more context to my question - I am fortunate to have a custom Mark Jacobs (mksj) Control System on my PM1340GT lathe and it provides 12VDC for Tachs and accessories. I was wondering if Mark does something with his control system or uses something external like a wall transformer.
 
When I build control systems, I real do not want others having to deal with wall warts and the confusion of multiple voltages and additional wiring. I standardize all my systems with a 24VDC power supply and a 12VDC step down regulator. This can be used for the relays, lights, tachs, etc. having to add yet another step down converter for the MachTach is a real pain, and requires extra wiring/cost for the 9V power. I try to keep my Tach enclosures to a minimum size, so heat generation/heat sink is also a problem. On the MachTachs I either add a heat sink, or I add another step down converter. I try to minimize wires and cables, so when it works out I will integrate each subsystem connections into a single cable. I have one 240VAC power cable to the machine which then provides power 240, 120, 24, 12V etc. to all the subsystems.

The MachTach uses an older style linear voltage regulator which dissipates excess voltage by generating heat. So anything above 9V and the regulator will not last w/o a heat sink (and even with that it generates a lot of heat). Nowadays with IC switching regulators with high efficiencies, one can input a wide range of voltages w/o the heat issues. I had some emails with the builder and indicated a drop in fixed 5V switching regulator as an alternative to the linear voltage regulator, the switching regulator has an input voltage range of 7-28VDC and is around 2.60 each. He will look into it, it certainly would make the kit easier to install in most VFD systems that use 12 or 24VDC power supplies. Since his design dates back for many years, inexpensive drop in switching regulators were probably not available back then. It is also the economics of the total parts costs.

When I get a request for an integrated tach build using my control systems, I have been putting the speed pot in the Tach housing which either mounts under the DRO or on the mill head. This puts the display/speed pot in a convenient location and you adjust the speed while looking at the tach. I have been using a compact military grade 3 turn Spectral potentiometer, which gives very nice speed control and fits well in the enclosure. I program the VFD for a lower and upper speed limit, so you get a very nice adjustable range. The Automation Direct 22mm speed pots are ok, but the speed pot used is not what I would consider a high quality unit. Long term, I have had failure of factory speed pots in some of the factory installed VFD machines, so I am always balancing the quality-cost equation.
 
mksj said:
When I build control systems, I real do not want others having to deal with wall warts and the confusion of multiple voltages and additional wiring. I standardize all my systems with a 24VDC power supply and a 12VDC step down regulator. This can be used for the relays, lights, tachs, etc. having to add yet another step down converter for the MachTach is a real pain, and requires extra wiring/cost for the 9V power. I try to keep my Tach enclosures to a minimum size, so heat generation/heat sink is also a problem. On the MachTachs I either add a heat sink, or I add another step down converter. I try to minimize wires and cables, so when it works out I will integrate each subsystem connections into a single cable. I have one 240VAC power cable to the machine which then provides power 240, 120, 24, 12V etc. to all the subsystems.

The MachTach uses an older style linear voltage regulator which dissipates excess voltage by generating heat. So anything above 9V and the regulator will not last w/o a heat sink (and even with that it generates a lot of heat). Nowadays with IC switching regulators with high efficiencies, one can input a wide range of voltages w/o the heat issues. I had some emails with the builder and indicated a drop in fixed 5V switching regulator as an alternative to the linear voltage regulator, the switching regulator has an input voltage range of 7-28VDC and is around 2.60 each. He will look into it, it certainly would make the kit easier to install in most VFD systems that use 12 or 24VDC power supplies. Since his design dates back for many years, inexpensive drop in switching regulators were probably not available back then. It is also the economics of the total parts costs.

When I get a request for an integrated tach build using my control systems, I have been putting the speed pot in the Tach housing which either mounts under the DRO or on the mill head. This puts the display/speed pot in a convenient location and you adjust the speed while looking at the tach. I have been using a compact military grade 3 turn Spectral potentiometer, which gives very nice speed control and fits well in the enclosure. I program the VFD for a lower and upper speed limit, so you get a very nice adjustable range. The Automation Direct 22mm speed pots are ok, but the speed pot used is not what I would consider a high quality unit. Long term, I have had failure of factory speed pots in some of the factory installed VFD machines, so I am always balancing the quality-cost equation.
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The output voltage of the LM 340 3-terminal regulator on the MachTach board is 5 volts. Max input voltage for the LM340 is 35 Volts. I just checked on my unit with the 9V @ 300 mA wall wart. Apparently, the no-load voltage of the wall wart happens to be 12.1 Volts, and when energizing the MachTach, the voltage still reads 12.1 V at 140 mA. The current demand at 9V using an external power supply still reads 140 mA. I have not yet installed a heatsink for the regulator, however, the stabilized tab temperature at both voltages is about 135 degrees F. Therefore, you should be able to run the MachTach at either 9 or 12 volts. I love those old 3-term regulators because they can take a beating and bounce back owed to internal therm cutout, they are easy to use, cheap, forgiving, and readily available.
 
Alan H said:
Blackjack thanks.

A little more context to my question - I am fortunate to have a custom Mark Jacobs (mksj) Control System on my PM1340GT lathe and it provides 12VDC for Tachs and accessories. I was wondering if Mark does something with his control system or uses something external like a wall transformer.
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Gotcha. I ran up some quick tests on my unit and it appears you can run your 9V MachTach at 12V without a problem. See my response to Mark.
 
mksj said:
The electrical noise issue was not the enclosure, but the shielded cable between the hall sensor and the MachTach. Convention would be to ground the shield at the source (not both ends), but any grounding of the shield (either end or at both ends) made the MachTach go wild. So if you use shielded cable, my recommendation is float it on both ends. Grounding is always one of those funny things, doesn't always work the way it is suppose to.

I would go with the hall sensor, you also only need a single magnetic to KISS. The IC hall sensor provided with the kit is a bit fragile, I used it on my lathe but wouldn't want to use it again if possible. You can get the cylindrical threaded type, NPN in 8 or 12 mm diameters. You connect the hall sensor brown power to wire to +IR, the blue negative to -RCV, and the black switched sensor line to +RCV. Works very nicely and no need for a pull down resistor.
Examples of sensors:
NJK-5001C
LJ12A3-4-Z/BX

Gear tooth sensor can be a bit more temperamental, you need the assembly he provides with the two capacitors in order for it to work correctly. At least he has it as an option. One problem on mills with a back gear, is you cannot take the tach off of the drive head, you need to pull the tack signal off of the spindle so need a very compact pickup assembly. One place where the small hall sensor is more desirable. On my mill which came with a factory tach, it uses an output from the VFD for speed and they also have a back gear sensor which rescales the tach range when in back gear. I recently build two integrated Halo Light and tach sensor for some PM 949 mills that where 1/4 thick and slid up on the mill ram. They required a very small hall sensor, it was very temperamental to magnetic flux.

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Yeah -- I think I will go with the Hall-effect sensor. After all, I already have it on hand. Thanks
 
Thanks Blackjack.

Here's a snippet from Mark's detailed response - "The MachTach uses an older style linear voltage regulator which dissipates excess voltage by generating heat. So anything above 9V and the regulator will not last w/o a heat sink (and even with that it generates a lot of heat). "

So my takeaway is that it appears best to feed the device what it wants without sending excess voltage up in heat.
 
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