well this is way off topic math

[rbig1]

Well I'm attempting to build a power hack saw. The motor speed is 1725 the drive pulley is 1.5" that would be 2587.5--. Then the driven pulley is 11" the end rpm would be 235.22. So I will have to add a jack shaft I"ll go with 1.5 pulley x 352.84-- will go with 11 inch driven pulley = 32.07---- rpm. This is where I get messed up the rotating assy is 3.5 long at shaft hooked to a 8" arm to blade. The blade is 14" long how many strokes will the blade make per min. Not sure how to figure strokes of blade. Any one like brain buster?? if I use same equations I come up with 14. Any math wizards. Looking to get 80 strokes a min or less. HELP........

[krispy]

Well, I think you are on the money to the point you get the 32.07 rpm. I'm not following the rest of the dimensions and mechanisms. The way I'm thinking of it, you would get 32.07 strokes each way with the blade per minute, one each way per revolution.

[slowrollwv]

Not good on math so I can't help. I would go to Harbor freight and get a small band saw. Or go to Grizzley equipment and see what I could find.

[baylensman]

If i'm following the length of the arms make no difference. it should 1 revolution of the final output gear regardless of its diameter soul be 1 stroke of the saw. kind of like the arm off the wheel of a locomotive, 1 complete revolution push the drawing rods into the piston then back out of the piston (i know the power works the other way but as a visual)

 

but as mentioned before a variable speed reciprocating saw with a metal blade or a portable band saw would do the same job cheaper and better IMHO

[Flyinfool]

This is the saw that I have. It works much better than a power hack saw. Much cleaner cut.

https://www.harborfreight.com/horizontal-vertical-metal-cutting-bandsaw-93762.html Then use a 20% off or better coupon on it.

The HF saw might even be cheaper than building a power hack saw yourself. On the other hand I fully understand the desire to build things even if it will cost more in the end, It is fun building things.

 

For your math the end answer of 32.07 RPM is correct, You are doing some extra steps that I do not understand what they are supposed to be, but you are getting the right answers.

 

As for strokes per minute, it will be equal to the rpm of the crank shaft. One revolution of the crank is one complete out and back of the blade. Just like a piston on the crank in your engine. I think you are trying to make the last part way more difficult than it is.

[rbig1]

jeff I just gave away saw just like that but was green. Would cut straight for 4 cuts then would make more grinding work to do. Also used a jet just like it it was just as irrating to use. Unckle had a power hack that i used to build gocarts with. Never had to squaire up cuts. Was slow as all get out though. So getting more than one bang out of building this. Always had to make design before building anything. Good memorys

[Flyinfool]

The instructions do not mention anything about adjusting the blade to make square cuts. But there are adjustments on the 6 bearings that hold the blade straight. Mine started to cut crooked when it hit around 20 years old. I had to replace and dial in the 6 blade tracking bearings and it was good as new again. I can not vouch for the quality of the newer ones. but when I look at them the castings for all brands of these small saws look to be from the same pattern, even tiny imperfections are the same in all of the brands. I do not know if the complete saw is made identical for all brands or just that they use the same raw casting. But if you look at the pics close, the only difference you see between brands is the color and the decals.

[rbig1]

Jeff you may want to open the gear box and put different lube in it. There known to destroy themselves. They get metal in the lube then grinds itself to death. Lost the jet one to that. Mine would not stay adjusted anymore. The blade quality I was buying was cheep which didn't help. It also got knocked over quite a bit. Casting never broke from abuse though.

[Flyinfool]

Now I have to go look, I don't think mine has a gearbox, it has step pulleys for a belt drive.