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Re: Understanding the PowerPro

#255312 by reible » Sat Dec 29, 2018 5:24 pm

Measuring the motor speed pulley is a little to advanced for me today. If I heat the garage again I might give it a go. Electric bill arrived and it was clear I was heating the garage a lot this past month, well I knew that since I was working on several projects but didn't expect to see the bill that high. So I have to conserve for a while.......

Ed

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{Knight of the Shopsmith} [Hero's don't wear capes, they wear dog tags]

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Re: Understanding the PowerPro

#255313 by dusty » Sat Dec 29, 2018 5:25 pm

The size of the Idler Shaft pulleys make no difference in this discussion. The pulleys on the idler shaft are both the drive pulley and the driven pulley in a three pulley arrangement (turning at the same speed. Therefore the ratio that counts is that between the motor pulley and the drive sleeve pulley. Thus the " idler pulley ".

PowerPro only.

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"Making Sawdust Safely"
Dusty
Sent from my Dell XPS using Firefox.

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Re: Understanding the PowerPro

#255317 by JPG » Sat Dec 29, 2018 6:31 pm

OK Dusty you initially asked for the dimensions of all three pulleys on a PP.

I maintain that RLF kept the original pulley parts(drive sleeve and idler) the same for compatibility reasons(both mechanical and documentation/manual wise).

As an attempt to get the third(PP motor)pulley dimension I worked back from the quill top speed(10,000) and sought an answer assuming a 5,000 rpm max motor speed.

My measurements of some idler pulleys and a couple of drive sleeve pulleys yield similar results(interestingly I have two sets of diameters for the idler pulley(2 each of 4 reading the same but slightly different from the other two which are also the same. A similar difference was measured at the bottom of the poly-v grooves.

Yes the idler does not enter into the motor/spindle speed derivation assuming the motor pulley is known. But it ain't known(yet) and that was what was being sought.

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Re: Understanding the PowerPro

#255321 by wa2crk » Sat Dec 29, 2018 9:34 pm

Just came from the shop and I tried to measure the diameters as closely as I could without tearing the machine apart. ( which I am not going to do at this time )
Motor Pulley 3.125 inches
Idler pulley 1.36 inches
drive sleeve pulley 1.9 inches

This would indicate an increase in speed between the motor speed and the idler shaft
But there is a reduction in speed between the idler shaft and the drive shaft by the drive shaft pulley being larger than the idler shaft pulley.
By making a slight adjustment to my measurements and using a measurement of 1.3 inches for the idler pulley and 2.0 inches for the drive sleeve pulley yields a ratio of 0.65/1 .
All measurements were taken by reaching into the headstock with digital calipers, so they may be off slightly, but I don't think by much.
Bill V
P.S. if the shaft speed is 10,000 RPM the idler shaft is 16,000 RPM. Dividing the idler shaft speed by 3.125" equals a motor speed of 6400 RPM
Making adjustments for normal stock sizes of pulleys (assumptions here)

Motor pulley 3.125 inches motor speed 6400RPM
Idler pulley 1.25 inches Idler shaft speed 16,000
drive sleeve pulley 2.0 inches spindle speed 10,000

Bill V

P.P.S All of this assumes that the pulleys on the idler shaft are the same diameter and that there is no step up in speed between the motor and the idler shaft.

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Re: Understanding the PowerPro

#255328 by dusty » Sun Dec 30, 2018 4:18 am

Thank you, Bill and JPG. I appreciate your efforts.

Your measurements and calculations to tend to confirm what John said. The step up ratio appears to be 1.6.

Your measurements and calculations do, however, introduce a question. What is the speed range of the motor used in the PowerPro. It has been stated (I have to research where) that the top DVR motor speed was 5500rpm. This translates to top spindle speed of 8800rpm. Thus a question.

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"Making Sawdust Safely"
Dusty
Sent from my Dell XPS using Firefox.

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Re: Understanding the PowerPro

#255330 by wa2crk » Sun Dec 30, 2018 7:44 am

Dusty
The only consideration is the ratio of the spindle speed to the motor speed. The ratio of the idler pulley to the drive sleeve pulley is 2.0 divided by 1.25 equals 1.6. So 10,000 RPM spindle speed would be 16,000 RPM auxiliary shaft speed. The ratio of the auxiliary sleeve pulley to the motor pulley is 1.25 divided by 3.125 equals 0.4. therefore the motor RPM is calculated by multiplying the 16,000 auxiliary shaft speed by the 0.4 ratio equals 6400RPM.
The ratio of the motor pulley to the drive shaft pulley is 2.0 divided by 3.125 equals 0.64. so 10,000 spindle speed times the 0.64 ratio equals a motor RPM of 6400 RPM

I don't know why the DVR motor would be limited to 5500 RPM. Theoretically it should be able to run as fast as the microprocessor can switch as long as the motor's armature is properly balanced.
Bill V

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Re: Understanding the PowerPro

#255331 by BuckeyeDennis » Sun Dec 30, 2018 8:14 am

wa2crk wrote:Dusty
The only consideration is the ratio of the spindle speed to the motor speed. The ratio of the motor pulley to the drive sleeve pulley is 2.0 divided by 1.25 equals 1.6. So 10,000 RPM spindle speed would be 16,000 RPM auxiliary shaft speed. The ratio of the drive sleeve pulley to the motor pulley is 1.25 divided by 3.125 equals 0.4. therefore the motor RPM is 16,000 auxiliary shaft speed times 0.4 ratio equals 6400RPM.
I don't know why the DVR motor would be limited to 5500 RPM. Theoretically it should be able to run as fast as the microprocessor can switch as long as the motor's armature is properly balanced.
Bill V


There are a couple of factors that limit the top speed of a motor.

First, motors all have a maximum “mechanical” speed. This is the limit above which the bearings may fail prematurely, or more likely that centrifugal forces exceed the structural strength of the rotor.

Second, high-frequency self-heating effects (from eddy currents) impose a thermal limit on motor speed. At some speed, to keep from overheating the motor, you have to reduce the motor current until the available output torque and power fall to zero. Running the motor that fast serves no useful purpose, of course, so the top rated speed is always somewhat less.

I have a Technatool DVR motor speed/torque curve that shows it can still produce about 0.9 hp continuously at 5000 RPM. So my educated guess is that Shopsmith chose to rate the motor for a higher speed, and settle for a lower continuous-power capability at top speed. This is entirely consistent with the reports of over-temperature alarms when routing at top speed for an extended period of time.

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Re: Understanding the PowerPro

#255333 by wa2crk » Sun Dec 30, 2018 9:11 am

Buckeye
You are correct that there other considerations. I believe that the mechanical limits can be met but the electrical limits are another consideration. Consider Formula One race car engines. Twelve cylinders and RPM of 14,000.
Another concern is the packaging of the Power Pro. The headstock is really crammed. Kind of like ten pounds of stuff in a five pound bag. JMHO
Bill V

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Re: Understanding the PowerPro

#255334 by reible » Sun Dec 30, 2018 10:15 am

I've seen the 50 to 5500 rpm number in the literature but I don't know how cast in stone that is.

Typical usage of the shopsmith for most operations should fall in the much lower numbers ie less then 4000 rpm of output. Things like sawing would benefit from having more power available.

I have nothing to back this up but I would think the planner might be the item that would require the most power so anyone have a better idea on this? A wide board and a deep cut??

Now when we get into different kinds of motors the rpm numbers can get quite high, router have top ends in excess of 30,000 rpm. Same for some other common tools, I've seen things that run at 70,000 rpm and I would expect that is no where near the top end of possibilities. I know the DVR mentions speeds of 10K but I believe that is a different model motor.

It would also be interesting to see where all this heat is generated. We have a power supply, a motor and then the drive train. And just how hot are we talking? We know that there is a thermal shut down that takes place to protect the system but no idea at what temperature that is and where it is measured.

Just a few thoughts.

Ed

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{Knight of the Shopsmith} [Hero's don't wear capes, they wear dog tags]

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Re: Understanding the PowerPro

#255335 by wa2crk » Sun Dec 30, 2018 10:35 am

When a current is passed through a resistance heat is generated. More current, more heat. All conductors have resistance. My original post was referring to mechanical considerations and pulley sizes. Heat generated by electronic components is another consideration as is a lack of an efficient fan. I have never used my machine at 10,000 RPM and probably won't. There is probably a fair amount of heat generated by the power supply. Switching power supplies run cooler but they still get hot depending how much they are stressed.
Bill V

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