Knife Grinder II

[gMike]

Here's what I have:

Dayton 1/4 hp 1725rpm motor (currently wired CCW).

The Lee Valley belt sander attachment (6" driven pulley, 3 3/4" idler pulley), 42" belt.

The problem:

The darn thing has a belt speed about 4 times what I would like (Probably about 3,500 ft/min)

The driven pulley can be easily changed (!/2" set screw). The idler pulley and mount will have to be replaced to change the pulley size.

I'd like to mount a smaller driven pulley (like 3- 4") and a bigger pulley as the idler. I suspect the idler needs to be about 6". That should hopefully cut the speed down to about 1,500-1,600 ft./min.

Does this sound about right? Check my thinking, which hasn't been any better than my typing lately.

Edit:
What do you call the crowned center pulleys?

[Isaac S]

Your current belt speed is about 2700 sfpm. A 3" drive wheel will give you 1350, and a 4" will give you 1800.

sfpm = (diameter of drive wheel in inches) x (3.14) x (motor rpm) / (12 in/ft)

The idler wheel has no bearing on the belt speed, so you may not need to replace it if you can adjust it to take up the slack created by the smaller drive wheel.

[TobyC]

Crowned pulleys.

[Timberwolf]

Quote:

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Crowned pulleys.

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Not "pulleys"...crowned "wheels"...is there even such a thing as a "crowned pulley"???

Second thought....a "flat belt drive" could be called a "pulley" I guess

[TobyC]

Timberwolf said:

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[blockquote]Quote:

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Crowned pulleys.

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Not "pulleys"...crowned "wheels"...is there even such a thing as a "crowned pulley"???

Second thought....a "flat belt drive" could be called a "pulley" I guess

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[/blockquote]

http://woodgears.ca/bandsaw/crowned_pulleys.html








http://chantlandpulley.thomasnet.com/cat...l-pulleys?

http://chantlandpulley.thomasnet.com/cat...d-pulleys?

[Timberwolf]

I got "V" pulleys stuck in my haid!!!!

[Timberwolf]

Mike, the drive wheel determines how many FPM the belt will rotate..A 2" diameter wheel will turn at ~900FPM..Just multiply the diameter by 3.1416 to get the circumference, then divide the answer by 12 and it will give you FPM...

The idler wheel makes no difference in how fast or slow the belt will travel.....I think the ideal speed for general sharpening is 900 to about 1500FPM...for making knives, the much faster speed is preferred {by me anyway} That's why a variable speed motor is ideal...but you can get good results with a stepped pulley drive system....however, a faster belt speed will require more power so a 1/2HP or larger motor would be better for a step- pulley-driven machine.

The crowned wheels are for belt tracking...to keep the belt centered, making it less likely to slip off while running. so they are called "tracking wheels"..and usually only one tracking wheel is required to make the belt stay centered. That can be a crowned drive wheel...

[enjuneer]

Please post some pictures so we can see what your sander assembly looks like. The picture on the LV site is from the motor side. I cannot see the pulleys.

Drive ratios and speeds are strictly geometry, so it shouldn't be too hard to change it. Another option, albeit more costly, is to switch the motor to one with a variable frequency drive (VFD). This will give you infinitely variable speed and make your sander infinitely more useful.

[Isaac S]

Is this the LV belt grinder you have?

If so, you may be able to drill a new set of holes in the bracket so that you can move the idler up. That depends on how much arm or bracket is inside the tube. If you go with a 3" drive wheel, I think you'd need to move it up about 2 3/8".

[Timberwolf]

Mike, if you can swap the idler with the drive wheel. you can slow the belt speed by approx 1,000fpm...or aprox. 1700FPM...As it is with the 6" wheel your belt speed is approx 2700FPM...That way you can still use 42" belts...