Bandsaw speed reducer build.

[Eddyde]

Hi All,
I recently picked up a nice mid 50's vintage, Boice Crane, 14" vertical bandsaw.

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.

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.

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?

 

[brino]

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

 

[f350ca]

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]

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]

brino

Thanks for the links, it's all helpful.

 

[Eddyde]

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]

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]

Thanks to the three day weekend I was able to make some headway on the bandsaw.

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.

At least it was an easy fix.

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

I was lucky and got a perfect friction fit of the keyway!

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.

After blasting.

I skipped taking some photos as the phone was elsewhere... I'll post more detailed shots when I do the final assembly.

The new motor on a hinged mount, made entirely from scrap.

The Machtach and the VFD confirm my spreadsheet calculations about 80 FPM at 20 Hz.

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

 

[brino]

Eddy,

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

-brino

 

[Eddyde]

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...