Shopsmith Forums

This has grown to be a long thread so I'll summarize here...

Based on how the machine has behaved and gut instinct as much as anything else, I don't think it's a belt or the clutch slipping; it truly seems like the motor just lacked sufficient power and bogged down or began to stall. When I installed the the sanding disk and tried turning it whilst holding the motor sheave, I could get to the drive sleeve clutch to slip, and while I did not measure the torque, based on the fact that I could bring the motor to a full stop when ripping I don't think the clutch is slipping prematurely. The motor just seemed unable to cope with the load.

The (edited to add: 9") thin-kerf HSS combo blade I inherited with the machine would bog the motor down whilst ripping but plows through a 2x4 just fine in crosscut, suggesting that the blade is a contributing factor (perhaps a big contributing factor). There seems to be significant drag when ripping and the blade is fully in contact with the wood.

The power cord had been replaced at some time in the past with a 16 ga (at best) replacement. I installed a new 14 ga cord of the same length and the motor power seems markedly better. Whereas before it struggled to rip a 1' section of 2x4 in 20 seconds, with the new cord 13 is easily achievable.

So my preliminary conclusion is that my problem was a combination of a sub-optimal blade creating excessive drag and an undersized power cord not supplying sufficient current.

My plan at this point, having improved the current flow, is to invest in a better blade (or blades).

Thanks everyone for the help & insights!

One question that I do not recall being asked, is what size blade is the combo blade?

just my .02 I went to a smaller dia and thin kerf blade and it has helped a great deal , I mainly use hard wood like oak and hickory / ash /walnut /maple .we have cut some fairly thick hickory over the last couple years with out a issue, as long as we slow down the feed rate and the saw speed we dont have much of a issue , I had issue with drift a while back but when I checked I realized the wood had a higher moisture content and the thin kerf blade wanted to follow the grain and bind . also the cord dia and cord length {and} the circuit amp will make a difference . right now I am using a #10 wire 25 ft cord on a 20 amp circuit with {5} 8ft led light strips with out issue . our motor is 3/4 hp 120v , keep the dust in the head stock blown out and do routine oiling as described in the manual and you should be good for many years . JMO

JPG wrote: Thu Nov 04, 2021 11:55 am ...On one occasion, I ran a headstock on a #12 (? foot) cord outdoors to plane some oak. It was for sure over 50 foot long.

The increase in startup to speed time was very obvious.

As for 100' runs in a house, IIRC earlier someone stated that runs over 100' require increasing the branch wire to the next larger size according to 'the code'...

Read that on the long extension cord and thought an experiment was in order. My conventional 1-1/8 HP 'Mark 4' was plugged in its normal spot very near the panel, so house wiring IR loss was minimal. I started it up on "Q" with a saw blade. Despite not starting at Slow it starts up pretty quick, less than two seconds. I added a 50' 12 AWG extension cord in line and the difference in startup time was negligible, probably could be measured but subjectively unchanged. Put a second 50' 12AWG in line, 100' total, and startup time was noticeably longer. I estimated 3 seconds. No issue there, in my mind, but definitely slower to start.

YMMV. Put 100' of 12 AWG house wiring ahead of the extension cord and even a short extension cord would likely make a noticeable difference. Or 99' of 14 AWG? Much worse, I think.

In my shop the conventional headstock reaches saw speed in about half the time of the PowerPro.

- David

DLB wrote: Fri Nov 05, 2021 9:33 am Read that on the long extension cord and thought an experiment was in order. My conventional 1-1/8 HP 'Mark 4' was plugged in its normal spot very near the panel, so house wiring IR loss was minimal. I started it up on "Q" with a saw blade. Despite not starting at Slow it starts up pretty quick, less than two seconds. I added a 50' 12 AWG extension cord in line and the difference in startup time was negligible, probably could be measured but subjectively unchanged. Put a second 50' 12AWG in line, 100' total, and startup time was noticeably longer. I estimated 3 seconds. No issue there, in my mind, but definitely slower to start.

YMMV. Put 100' of 12 AWG house wiring ahead of the extension cord and even a short extension cord would likely make a noticeable difference. Or 99' of 14 AWG? Much worse, I think.

In my shop the conventional headstock reaches saw speed in about half the time of the PowerPro.

- David

Thanks David. That is a very interesting experiment and I believe your results. The challenge that I have is in understanding how it might affect the motor performance under load. I am an EE and understand the basics of motor design, but I don't have experience in designing motors first hand. The 100' total extension cable that you used should have lowered line voltage say 5%, so if you had 120V at the panel you would be looking at 114V at the motor. Not bad, in my opinion, considering 110V used to be the standard for electrical distribution in the US. For light load, I believe a 10% reduction in voltage will cause a corresponding 10% increase in current draw of the motor. This is fine until you get to heavy load where a voltage decrease may put the motor current draw outside of the max rated amps for the motor. So, getting up to speed on startup is delayed with lower line voltage. However, I am still trying to understand how once the saw is spinning, at speed, and it encounters a heavy load how a 5% or even a 10% reduction in voltage affects the ability to make a cut. In researching this a bit, I believe it is due to the torque characteristics of the motor, i.e. the breakdown torque for AC induction motors is proportional to the square of the voltage applied. So, a 10% reduction in line voltage equates to a much larger 21% increase in the slip amount. Anyone experienced in motor design agree with this? I am just curious about the mechanism involved here and trying to understand it. In the future, for anyone that reports an issue like this, I guess we should a) encourage minimum IR drop (minimizing/eliminating extension cables) and b) asking the owner to check their line voltage in their shop. The latter being important to know because they will be more susceptible to even a small IR drop in their machine's performance. Of course, there are still other factors as previously mentioned such as sawblade sharpness, belts slipping, etc. I know this has been the recommendation of the experts on the forum for some time, but I am just trying to figure out the "why" behind this recommendation.

HopefulSSer

Thanks for summarizing the problems as you see them. I think you have a good idea of what is going on. JPG asked about the size of the blade. A 10" blade is commonly used on the Mark V but originally the Mark 5 used a 9" blade and that continued into the early 1960's. It was around the same time as the Mark 5 went from the 3/4 HP Motor to the 1-1/8 HP Motor and the introduction of the Mark VII that the 10" blade became available from Magna American. When you get a new blade let us know how it worked and try using both a "normal" set up with the blade out just above the wood and having the blade at maximum height with less blade surface contact in the wood. I'm just curious.

JPG wrote: Thu Nov 04, 2021 8:57 pm One question that I do not recall being asked, is what size blade is the combo blade?

That's true we haven't talked about that. It's 9" and I edited the post above with that just to keep all the info together. Thanks! Will keep you all posted!