Vintage bandsaw motor failure

[Mikael Norlén]

Hi,

I recently bought an old 16" German bandsaw, Frommia Bs 398. It is my first bandsaw and I'm still learning. As I started sawing I hadn't set the blade alignment pieces close enough to the blade, it got stuck and the motor died. After investigating the problem I found that the motor shaft had completely broken. See attached pictures.

When researching the problem I found a recommended blade speed of 3800 SFPM for a 16" bandsaw. As the saw does not have a pulley system installed this gives me a recommended motor RPM of 908. https://www.finewoodworking.com/foru...comment-326712

After also talking to a mechanic there seems to have been several issues with the old motor setup. As the motor appeared new, it must've been recently installed by someone who knew little about the saw.

1. The old motor was running at 1400 RPM, 492 RPM above recommendation.
2. The shaft was a bit short, only coming through half of the wheel, then connected with a screw. The wheel itself also seems to have been pushed in just a bit deeper to accommodate the shorter shaft.
3. There is no pulley system installed to help with shock reduction.

They tell me that it is uncommon for a bandsaw motor to break in this way, even if the blade gets stuck. So I am wondering if simply replacing the motor will fix the problem.

Do you think the higher RPM and the questionable shaft connection could cause this type of failure, or could there be other issues involved? Is it ok for a bandsaw motor to run without a pulley system? From what I can tell the saw never had one.

Thank you so much for your time and suggestions!

[Chuck Saunders]

Sounds like wrong motor and over tensioned blade. Many bandsaws have direct drive, I don’t think that is the issue. The rubber tires are the shock absorber on a bandsaw. Motor speed being 50% over spec would make cutting speed undesirable.
Chuck

[Jimmy Harris]

I'd just replace the motor with something more appropriate. Shearing the shaft, cleanly like that, tells me there was something wrong with that motor to begin with. I've broken a lot of electric motors in my time, but I've never seen a shaft shear like that. Especially with how cleanly it broke, I'm really leaning towards a manufacturing error being the root cause.

[Bill Dufour]

Good luck finding a motor to fit. Is that one three phase? I would buy a three phase motor that fits and use a VFD to slow it down. Some older motors ran at 950 rpm.
If no luck finding a motor to fit make a drive shaft and belt drive that from whatever motor you like
Bill D

[John TenEyck]

I wouldn't second guess the rpm. If the manufacturer thought 1400 rpm was correct, then why challenge it? My 17" bandsaw runs at 4500 fpm blade speed. Some industrial ones run over 5000 fpm. Higher fpm allows you to cut faster, nothing wrong with that.

The motor plate looks old to me. It doesn't look like one on a new motor. In any case, you need a new motor. Looking at the saw frame, it looks like a face mount motor could be made to fit, though some new holes may need to be drilled. The bigger issue is mating up with the arbor hole in the wheel. I would look for a motor with a shaft that fits that wheel hole and is long enough to project to the far side of it. As Bill said, a VFD to slow it down to whatever rpm is desired would be the best option, so get a 3 phase motor.

John

[Andrew Hughes]

I remember seeing a shaft broken off next to the bearing before. Don’t remember where. I do remember it’s due to the bearing scoring the shaft. Possibly someone installed the wrong bearing.
Its a really cool looking saw hope you can get it fixed
Good Luck

[Rod Sheridan]

Hi, that’s a single phase 50 Hz motor, 1,400 RPM.

I’m presuming you ran it at 60 Hz so it would have been 1,680 RPM.

If you hadn’t changed the capacitor, if it has one, it may have had an electrical failure anyway.

An 1,800 RPM 3 phase motor could be operated at the correct speed by a VFD, you just need a 3 Kw one to compensate for the reduced speed.

Since 3 Kw isn’t common in NA, 3 HP should suffice.

Regards, Rod

[Brian Holcombe]

How do you all know where the OP is located? I am assuming Europe, finding a used Frommia saw in the US would be difficult to say the least, but pretty cool.

Personally, I would check to see that the modern version of that frame size (90L) motor has the same bolt hole pattern and shaft size (they should). If that's the case, I would find another 1400rpm version and use that.

In a 90L frame you can get 2.2kW which would be a decent upgrade from the 1.5kW.

I would probably get a 3ph motor and run it with a VFD if you don't have 3ph, that way you can adjust the speed a bit.

[Mark Hennebury]

You have a 1957 German bandsaw with an Italian motor on it, seems a little strange to me. May not be the original motor. You could have the shaft repaired or a new shaft made, but it would be very expensive, It is probably a lot easier and cheaper to replace the motor.
Frommia did make direct drive and belt drive, as in this 1977 manual.

Screenshot 2024-04-05 121120.jpg

[Mikael Norlén]

Thank you for your replies, much appreciated!

Yes, the saw is German, I am Swedish but live in Italy since a couple of years and bought the saw here from a general salesman who didn't know anything about the saw. As Mark says it seems unlikely that the motor is original as it is Italian. It also seems new. The only reason the plate looks a bit worn is because I had to scrape the paint off to be able to read it.

I see that the recommended SFPM in the post was originally given by Timberwolf, a blade manufacturer. I could see how FPM recommendations could vary a bit given:

1. Wheel diameter: A greater wheel diameter would naturally allow more speed as it requires less tension to stabilize the blade. This value is already included in the formula.
2. Frame construction: A sturdier frame could potentially allow higher tension, but could in turn also stress the motor and blade.
3. Blade. The shape and spacing of the teeth would be optimized for a certain speed. Timberwolf apparently mentioned that you should not stay more than 400 FPM above/below recommended values (~+/-10%) to avoid compromising gullet function.
4. Task. Perhaps cutting thin boards could benefit from higher speed, while heavier resawing benefits from more torque.

The EU/Italian standard is 50 Hz so the motor was running at the specified 1400 RPM. However, in hindsight, in spite of my lacking experience, I would say that it felt way too fast, almost like the whole saw was vibrating. Also, given the motor shaft failure, it probably required too much tension to make the blade run in a straight line.

We know that the saw was designed for a motor with:
- Shaft diameter of 24mm given the hole in the bottom wheel.
- Flange fastened with 4 bolts with 11.5 cm spacing.

This seems to correspond to a single phase MEC 90 B 14 motor I found on ebay.

Basically they have two interesting options:
1. 1.5HP, 6 pole, 900 RPM
2. 3HP, 4 pole, 1400 RPM

The 1.5HP motor seems to be the obvious choice. From what I understand, if I would add a device to lower the RPM of the 3HP motor, I would also reduce the power linearly and arrive at 3 * 900/1400 = 1.93 HP. I'm not sure it seems worth it. These are the highest HP motors I found to fit the 24 mm shaft. For three-phase I found like 0.5HP higher.

I do want to use the saw for resawing thicker stock at times. The max resawing capacity of the saw is 30 cm (11.8 inch). I know I will want to resaw some 20-25 cm douglas fir and pine for our house project. Do you think it would still be fine at 1.5HP? Or do you have any other suggestions for increasing the power of the motor?

All the best from Italy, Mikael

[Brian Holcombe]

Resawing 10” material takes some HP, I would opt for a 3ph motor in 3hp and run it with a vfd. This gives you the option to run it faster if need be.

[Tony Shea]

I would also recommend finding a 3hp motor that runs on 3 phase. Typically these can be found slightly cheaper than a single phase motor. 3 phase motors don't require start capacitors or centrifugal switches therefore are slightly a bit easier to manufacture. Pick up a VFD, be sure to de-rate the VFD if you'll be feeding it with single phase, and you'll have amazing speed control. You will be so happy to have simple speed control on a bandsaw with just a press of a button with infinite adjustment. Be sure to research the size vfd you'll need. As I said above feeding a VFD with single phase requires installing a larger size VFD than the motor rating. I believe the rule of thumb here is up-size the VFD 175%, but please research this as this is off the top of my head.

[Bill Dufour]

Where does Douglas Fir come from in Italy? It is native to western North America and very common here in lumber yards. Is it grown in Europe?
Bill D

[Bill Dufour]

I would consider keeping the old motor. Pull out the rotating bits and make a new shaft, extra long on both ends. Bolt it in place and add a pulley on the outboard end and use a belt drive from a motor to get any rpm you want.
Bill D.
PS: you have excellent English

[Mikael Norlén]

Ok I see, both options are interesting. I'll think I will have to look into how this pulley system could be set up a bit..

Yes, for me Douglas is exotic, but it was actually grown here in the Apennine mountains. I don't think it is especially common though. Last time I was at the lumberyard they told me most of the oak was imported from America. Otherwise Swedish pine is still going strong for construction. Larch from the Alps and chestnut seems popular in Italy and is great for outdoor use.

Thank you, I've been traveling a lot and working on the web so I'm used to English, + Swedes learn it in school more than most other countries. Have a great weekend.