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Re: How much power should I expect?
Posted: Wed Nov 03, 2021 8:16 am
by RFGuy
Here we go again. I raised the question on some previous threads regarding how much is lost to the variable transmission, i.e. sheaves in the Mark V. At one point, I thought it was determined to be about 30% power/torque loss from it on another thread. Friction losses typically amount to about 10-15% loss for a typical 2 pulley system, or at least I found this somewhere else online. IF that is correct, then the Mark V headstock is a 3 pulley system so it stands to reason that the losses could be at least 20% or more for it. This is the main factor that is different from "other" tablesaws and a Shopsmith. They are 2 pulley systems and Shopsmith is a 3 pulley system, hence Shopsmith equipment will have more friction losses as a result. There is no free lunch. Having a variable transmission as a feature has a cost in terms of power loss in my opinion. Now, someone will come in and disagree with this stating very little power is lost in the Mark V transmission and that all that matters for ripping a 2x4 on a Shopsmith is torque.
Since we don't have any data, or even hand analysis, on how much power loss occurs in the Shopsmith variable transmission, I tend to believe real world experience like lahola1 indicates here. There is something different with a Shopsmith when it can't properly rip a 2x4 when a cheap, underpowered contractor tablesaw has no issues with it.
Re: How much power should I expect?
Posted: Wed Nov 03, 2021 8:29 am
by dusty
RFGuy wrote: Wed Nov 03, 2021 8:16 am
Here we go again. I raised the question on some previous threads regarding how much is lost to the variable transmission, i.e. sheaves in the Mark V. At one point, I thought it was determined to be about 30% power/torque loss from it on another thread. Friction losses typically amount to about 10-15% loss for a typical 2 pulley system, or at least I found this somewhere else online. IF that is correct, then the Mark V headstock is a 3 pulley system so it stands to reason that the losses could be at least 20% or more for it. This is the main factor that is different from "other" tablesaws and a Shopsmith. They are 2 pulley systems and Shopsmith is a 3 pulley system, hence Shopsmith equipment will have more friction losses as a result. There is no free lunch. Having a variable transmission as a feature has a cost in terms of power loss in my opinion. Now, someone will come in and disagree with this stating very little power is lost in the Mark V transmission and that all that matters for ripping a 2x4 on a Shopsmith is torque.
Since we don't have any data, or even hand analysis, on how much power loss occurs in the Shopsmith variable transmission, I tend to believe real world experience like lahola1 indicates here. There is something different with a Shopsmith when it can't properly rip a 2x4 when a cheap, underpowered contractor tablesaw has no issues with it.
Yup, here we go again. Yes, pulley systems are characterized by some level of power loss but that loss IMO is not due to the variability of those pulleys.
Re: How much power should I expect?
Posted: Wed Nov 03, 2021 8:34 am
by RFGuy
dusty wrote: Wed Nov 03, 2021 8:29 am
Yup, here we go again. Yes, pulley systems are characterized by some level of power loss but that loss IMO is not due to the variability of those pulleys.
It is not the variability of those pulleys, but the mere fact that a Shopsmith system has a 3rd pulley that adds more loss. Having the variable speed "feature" causes more power loss because of the additional pulley system.
Re: How much power should I expect?
Posted: Wed Nov 03, 2021 8:42 am
by dusty
RFGuy wrote: Wed Nov 03, 2021 8:34 am
dusty wrote: Wed Nov 03, 2021 8:29 am
Yup, here we go again. Yes, pulley systems are characterized by some level of power loss but that loss IMO is not due to the variability of those pulleys.
It is not the variability of those pulleys, but the mere fact that a Shopsmith system has a 3rd pulley that adds more loss. Having the variable speed "feature" causes more power loss because of the additional pulley system.
Totally agree even though only one output shaft is loaded at any given time..
- Sheaves and Shaft a Comparison.jpg (150.54 KiB) Viewed 1418 times
Re: How much power should I expect?
Posted: Wed Nov 03, 2021 9:11 am
by JPG
The greater size(diameter) than most pulley arrangements increases the amount of contact with the belt and resultant frictional drag. The amount of heat generated is an indication of that. Then there is the squeezing going on.
Re: How much power should I expect?
Posted: Wed Nov 03, 2021 9:43 am
by HopefulSSer
HopefulSSer wrote: Tue Nov 02, 2021 9:09 pm
1. SS power cord (original? it does seem perhaps a bit small) plugged directly into the wall socket. Wiring panel to socket is 14/2. Probably wouldn't be the worst thing to replace the current power cord with something a size larger.
Correction -- I recall now that when I went into the power head for service I found the remains of a prior power cord so the current one (though old) is not the original. Maybe it's a SS replacement part, maybe it's not. Who knows? But a fresh one, one size up, seems in order!
Re: How much power should I expect?
Posted: Wed Nov 03, 2021 9:49 am
by HopefulSSer
JPG wrote: Wed Nov 03, 2021 9:11 am
The greater size(diameter) than most pulley arrangements increases the amount of contact with the belt and resultant frictional drag. The amount of heat generated is an indication of that. Then there is the squeezing going on.
<lightbulb> Now that y'all mention that, yes there is definitely power loss in the belts -- notice how hard it is to turn the quill by hand. All the individual components of the driveline spin easily & freely on their own, including the motor. I'm going to Lowe's to see if they have something suitable for a power cord. While I'm there I'll try turning one of their contractor saws for comparison.
EDIT: Bummer. None of the saws had blade (as I expected -- liability problems) but they also all had lower blade guards blocking access to the arbor. Test failed.
Re: How much power should I expect?
Posted: Wed Nov 03, 2021 10:26 am
by DLB
Each bearing also has a parasitic loss that increases with speed. The SS power system has more ball bearings than a typical portable table saw. No free lunch here either. But IMO the total losses are pretty low up to and including TS speed. Most modern portable TS's advertise a 15 Amp motor (don't get me started) and I'm happy to agree that it is likely that they produce more power at the blade than a convention SS Headstock. Acknowledging that input Amps are not input power and input power is not output power.
Getting back to the OP's questions though. I feel like the chances that his headstock is producing less than normal power are somewhat lower than the chances that his older HSS combo blade is needing more than normal power to rip 2X pine. Nothing against HSS blades, I know they can be very good when sharp, but most of the community has moved to carbide blades for their many inherent benefits. IIWM I'd replace the blade as the most likely culprit. Money is always a consideration, so selecting the best option depends on many factors. Almost any new carbide rip or combination blade should be sufficient to determine if the blade is the cause of the problem. Recommendations are different based on the goal and whether or not a 5/8" arbor is currently in play.
- David
Re: How much power should I expect?
Posted: Wed Nov 03, 2021 10:38 am
by HopefulSSer
I'm tending to agree with David. I do think the new power cord will help -- it certainly won't hurt and may be a contributing factor. If nothing else I'm sure it's safer. But the more I play with it the more I think the primary culprit is the blade. And again, as I noted above, I observed yesterday that this same blade with chew through a 2x4 in crosscut, no problem.
The goal is just general all-around use. (The next thing on my horizon is ripping some 1-by to width and rabbeting it to replace some damaged t&g ceiling boards on the back porch. So mostly ripping cuts but also some crosscutting as I cut them to length. In future I want to do more turning so sawing blanks for that will be a big use for the saw. (I wish a bandsaw had come with it!)
There's no 5/8" arbor in play but they seem attractive. There's a certain appeal to me in being able to use any commonly available blade. Am I wrong in that?
Re: How much power should I expect?
Posted: Wed Nov 03, 2021 10:47 am
by RFGuy
HopefulSSer wrote: Wed Nov 03, 2021 10:38 am
There's no 5/8" arbor in play but they seem attractive. There's a certain appeal to me in being able to use any commonly available blade. Am I wrong in that?
Shopsmith sells a 5/8" arbor for 5/8" bore size sawblades. Just make sure you get the right one for your particular vintage of Mark V. I can't remember which one you said you had, otherwise I would post the part # here. They have both the 5/8" and 1-1/4" arbor sizes for tablesaw blades. You can use any commercial sawblade with it. I'd also recommend starting with a new blade first as well. JMO.