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Bandsaw speed reducer build.

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Eddyde

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#1
Hi All,
I recently picked up a nice mid 50's vintage, Boice Crane, 14" vertical bandsaw.
IMG_2493.jpg IMG_2494.jpg IMG_2495.jpg IMG_2501.jpg IMG_2504.jpg IMG_2537.jpg IMG_2538.jpg
It has a three phase motor so I figured I'd simply throw a VFD on it and be able to get down to metal cutting speeds, wrong!... The motor is rated at 1150 rpm and running it at 15hz only gets the blade down to 1000 FPM, any frequency below that, the torque loss is too great and the blade is easily stalled. That speed is okay for aluminum but still too fast for steel. So I came to the conclusion, I must fit a speed reducer on it to get to a slow enough speed range and have adequate power to cut ferrous metals. Being the saw is direct drive I'll need to move the motor lower in the cabinet and install a shaft and pulley arangement in its place. However, pulleys alone won't get the blade slow enough, it needs a gear reducer as well. That's fortunately been solved by a serendipitous catch of a thread here on HM about a "Pull Gear" 7:1 pulley speed reducer and the chance I was able to grab one off eBay for cheap.
So far, I had to make a custom puller to get the drive wheel off the motor shaft.
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I have also purchased flange mount bearings, shaft etc. from Mcmaster Carr and started construction on a mounting bracket (pictures soon).
Right now, My dilemma is the calculating the speed ranges I have a couple of options, I threw together a spreadsheet to help.
Speeds.jpeg

The "pull gear"7:1 reducer has three pulleys on it (2.75" 3.75" and 4.75") and can be locked out for a 1:1 ratio, it will be mounted to the motor, the larger pulleys mounted to the drive wheel shaft.
The red line is over the saws original blade speed of 4200 FPM, so I am leaning towards the larger set as it won't over speed and I'll get some very low speeds if needed. I have checked bandsaw speed charts and some go down the 50 FPM for cutting hard steels, has anyone really cut this slow, is it really worth having the capability?
 

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brino

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#2
Hi Eddy,

I am watching your thread!

This thread: https://www.hobby-machinist.com/threads/any-difference-wood-or-metal.63388/
recommends 50 fpm for stainless.

Here's another take on a similar mod:
https://www.hobby-machinist.com/threads/wood-metal-cutting-band-saw.40752/post-429497

https://www.hobby-machinist.com/threads/bandsaw-project.31960/#post-271727
https://www.hobby-machinist.com/threads/slowing-down-the-band-saw.38093/

There was one more thread I tried to find where someone used a worm gear speed reducer.......but can't seem to find it.

Thanks for sharing it.
-brino
 
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f350ca

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#3
Can you reuse the original 1150 rpm motor, would get you a little slower at the same frequency. I have an old Delta Milwaukee that uses a gear reducer and 4 step pulley for metal. Gets down to about 100 fpm, great for steel but will eat a blade pretty quick if you need to cut stainless.

Greg
 

Technical Ted

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#4
Interesting. I recently picked up a 1955 Boice Crane, 14" vertical bandsaw myself, but the reason I got it was because it had the 4 step cone pulley with 2 range gear box. I put it in the slowest speed when I first got it and haven't changed it, since I already had a wood cutting vertical bandsaw. On the outside, it looks almost identical to yours.

Here's a link to my earlier post on it: https://www.hobby-machinist.com/threads/boice-crane-model-2309-14-vertical-bandsaw.60208/

Ted
 

Eddyde

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#6
Can you reuse the original 1150 rpm motor, would get you a little slower at the same frequency. I have an old Delta Milwaukee that uses a gear reducer and 4 step pulley for metal. Gets down to about 100 fpm, great for steel but will eat a blade pretty quick if you need to cut stainless.

Greg
At first, I was planing to use the original motor however, it has a 1" shaft and the speed reducer is for a .750" shaft. If I make a male female adaptor, the combined length will be to long to fit in the cabinet. I could dissemble the motor, chuck the rotor in the lathe and make it .750"but I would also have to make a special bracket for it as it's a face mont style. I suppose could also add a counter shaft but all in all its a lot of work. Meanwhile, I have an almost new 1 HP Baldor sitting on the shelf. So with that motor I'll get down to 80 FPM at 20hz, I might be able to go even lower frequency as the Baldor is higher HP than the original ¾ HP, we'll have to see...
 

Eddyde

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#7
Interesting. I recently picked up a 1955 Boice Crane, 14" vertical bandsaw myself, but the reason I got it was because it had the 4 step cone pulley with 2 range gear box. I put it in the slowest speed when I first got it and haven't changed it, since I already had a wood cutting vertical bandsaw. On the outside, it looks almost identical to yours.

Here's a link to my earlier post on it: https://www.hobby-machinist.com/threads/boice-crane-model-2309-14-vertical-bandsaw.60208/

Ted
Thanks for the link. Yes they are basically the same machines except for the gear & pulley reduction. I was hoping to find a smaller bandsaw already capable of metal cutting speeds but they seem few and expensive. When this came up for a near scrap price, I figured it was "the one"...
 

Eddyde

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#8
Thanks to the three day weekend I was able to make some headway on the bandsaw.
IMG_2766.jpg

First issue, the original motor shaft isn't 1" like I thought, it's 63/64ths? so the new shaft wouldn't fit into the bore of the drive wheel.
IMG_2739.jpg

At least it was an easy fix.

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Then I had to make a shaft adapter to get the Pull Gear to fit on the new motor

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I was lucky and got a perfect friction fit of the keyway!
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Making the bearing support, first I drilled and tapped the holes in the base plate then tack welded the supports and upper plate in place then drilled and tapped the upper holes. I was thankful for the DRO on that job.

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After blasting.
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I skipped taking some photos as the phone was elsewhere... I'll post more detailed shots when I do the final assembly.
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The new motor on a hinged mount, made entirely from scrap.
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The Machtach and the VFD confirm my spreadsheet calculations about 80 FPM at 20 Hz.

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Cut some 5/16 plate like butter... Now to take it all apart, tweak a few things and reassemble it for keeps...
 
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brino

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#9
Eddy,

Nicely done! I had never heard the term "Pull Gear" before this thread.
Thanks for taking us along for your build!

-brino
 

Eddyde

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#10
Eddy,

Nicely done! I had never heard the term "Pull Gear" before this thread.
Thanks for taking us along for your build!

-brino
Thanks Brino,
Before I embarked in this mission I had never heard of the Pull Gear either. Ironically, I imagined something like it whilst searching for a gearbox, then discovered it on T. J.'s thread. It is the perfect solution! I'll bet there is a market for them, patents long expired...
 
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Eddyde

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#11
I completed the final assembly of the bandsaw. Here are some details (click images to expand):
IMG_2899.jpg
I had to reduce the width of the hub on the middle pulley so it would fit closer to the large pulley and be in line with the grooves on the Pull Gear (drive pulley).
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The slice of hub and an additional shim, fabricated from a washer, will be used as spacers between the middle and small pulleys.
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I had to tilt the axis of the hub so I could drill hole for the setscrew that was obliterated when I cut it down.
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A long tap cost over $35 so, I let the drill cut a shallow notch in the rim aiding alignment of a regular tap, which I was able to turn with an open end wrench.
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The bearings, shaft & pulleys test mounted on the bearing support
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All fit perfectly well.

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The cabinet interior showing the original motor location and the strut channel for the new motor mount.
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The bearings shaft and support bolted in.
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The motor mount, The shaft has shoulders so it has almost no play between the angle supports. I added the flat on the end incase I wanted to eventually mount a lever to aid in changing the belt on the pulleys.
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Routing the tachometer and control cables was a chore. The frame of the machine is fabricated welded steel plate, with lots of cross supports. I made this hole with a drill and die grinder.
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Upon cutting the hole for the control panel I discovered one of the several cross supports in the column. Luckily they had holes bored in them so I was able to snake the cables down to the motor compartment. I was able to cut this one out of the way with the plasma torch.
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The Tachometer read head, cable guard and the inner bearing.
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The drive wheel, reflective tape markers and Tachometer read head.
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The control panel ready to install. I used a three turn potentiometer for finer speed control.
The Tachometer (MachTach) and control panel installed.
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The MachTach and control panel installed. I made a custom knob for speed control.
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The motor, VFD and pulleys mounted.
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The motor and Pull Gear speed reducer. The threaded rod prevents the outer part of the PG from turning when in speed reduction mode, it is removed and the hub locked to give full speed, no reduction.
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The lower switch powers the VFD and MachTach.

The machine cuts very well, with plenty of power in the low speeds and the blade tracks easily. All in, I have about $350 and about 30 hrs. of work invested. I will be doing a couple of refinements and some touch up paint in the future but for now it's ready to work, so I am happy :)
 
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