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Band saw conversion

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Speedy Builder530/11/2010 19:35:04
2878 forum posts
248 photos
I have a DEWALT DW738 woodworking bandsaw - a good bit of kit.  It has a blade speed of 330 and 800 m/min.
 
For steel I need about   30 - 40 m/min.
 
I would like to retain both wood and metal cutting capabilities.
 
The motor is a 2830 RPM 240volt motor that I am told can't be speed controlled.  There is not an easy way to put reduction gears/ pulleys within the cabinet,  Replacing the motor with a fully speed controlled motor would probably be too an expensive an option.
 
Has anyone had a similar problem and a soloution to it. 
Ian S C01/12/2010 12:00:08
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7468 forum posts
230 photos
Don't know the unit, but would a 1/4 hp 1400rpm/ 4pole motor fit (here in NZ They are as cheap as chips $NZ20 second hand), that takes you to 165 m/min, it then needs the pullies changed to further reduce the speed. Ian S C
Speedy Builder501/12/2010 12:15:29
2878 forum posts
248 photos
Good idea Ian, but the motor pulley is already about as small as you can get it,  and the large pulley can't get bigger.  It would need a complete re-hash of pulleys mounted outside of the bandsaw chassis, however I like the idea of the 1400 rpm motor.
Bob
Clive Farrar01/12/2010 12:24:44
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125 forum posts
41 photos
See what you mean there is not much depth to one of these,we have one at work.
 
As i see it the only way to get down to the speed you want is to sort out pully changes.
 
I have an old Burgess one that has a roundthane drive belt 6mm dia and a pair of three step pulleys that give me metal wood and sanding speeds.  they are about 40 mm thick and probalby 120 mm od max.
 
Do you think you could replace yours with something similar? I can take a photo if you want.
 
Regards Clive 
Clive Farrar01/12/2010 12:28:28
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125 forum posts
41 photos
you say you can not speed control it but I would have thought you could use a dimmer switch to provide a variable voltage.
 
I guess the big problem would be that it would drop the torque to much and make cutting a very slow process.
 
Nowt to stop you trying it though.
 
regards Clive
Gordon W01/12/2010 14:57:43
2011 forum posts
Did something similar, on a different sort of machine, years ago, this involved making up a counter shaft and two pullies, same idea as old lathes etc, Given the cost of new ones it might be cheaper to own two saws.
Dunc01/12/2010 14:59:14
139 forum posts
Have a look at http://books.google.com/books?id=RdMDAAAAMBAJ
 & navigate to the November 1943 issue
Compact Jackshaft On Motor For Multi-Speeds, Popular Mechanics, Nov 1943
 
This jackshaft mounts directly on the motor.
Stovepipe01/12/2010 16:30:36
196 forum posts
I've also got a DeWalt 738 bandsaw. There is (was?) a DeWalt739 which is a variable speed version, but I don't know what motor/mechanism was used. Anyone know ?
 
Dennis
Speedy Builder501/12/2010 18:14:26
2878 forum posts
248 photos
Just checked, DEWALT 739 varies speed between 330 and 800 M/min.
 
Cor,  eventually found the Pop mech Nov 43 article - good idea.
 
Speed control was dismissed in an earlier request for information as the power would deminish long before the speed did, leading to burn out.  My motor is 750w (about 1 Hp).
 
But thanks for trying guys.
 
Bob
Peter Tucker01/12/2010 18:25:17
185 forum posts
Hi Robert,
 
My fatherinlaw used a worm drive to convert his bandsaw.  unfortunatly he's dead and the saw is long gon so I can not see how it was done.
 
Good luck.
 
Peter.
Ian S C02/12/2010 01:18:15
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7468 forum posts
230 photos
Robert, if you don't mind it being fixed to the bench, how about fitting the motor under the bench with a counter shaft, still try and use a 1400rpm motor, I feel that for driving machinery the lower reving motor gives better power ie., higher torque, also smaller pullies. Peters' idea is another possibility, if you come across a reasonably priced (or freeby) right angle box, if the ratio of the box is wrong a belt drivebetween either the motor and box, or the box and saw should fix that. Ian S C
Chris Banninger02/12/2010 04:37:30
12 forum posts
> There is (was?) a DeWalt739 which is a variable speed version, but I don't know
> what motor/mechanism was used. Anyone know ?
 
I have a DeWalt 3501 which is the same as the DW 739 but for another market. It has a 0.55kW induction motor of 2850rpm. Variable speed is by an adjustable cone V-belt pulley on the motor shaft. By changing the motor tensioning via a handle, the cones of the pulley open or close (just like the Dutch DAF cars did it 40 years ago). Speed range is 330 to 800 m/min.
 
I tried  to cut non ferrous metal with this bandsaw. The only serious problem is that the metal chips get embedded in the rubber tyres and are very difficult to remove from there and damage the tyre, eg cut into the tire. If used for metal, this bandsaw will in my opinion only have a very small fraction of the lifespan when used for wood and plastics.
 
This machine is made for DW in Italy. I live in Australia and it would be very difficult for me to obtain any spare parts for it. So I rather use it for wood and plastic only.   
 
Chris
ady02/12/2010 09:09:35
612 forum posts
50 photos
Maybe you could try and knock up a backgear style system on your pulleys with the lathe?
Billy Mills02/12/2010 12:25:35
377 forum posts
Agree with Chris, Metal cutting bandsaws are different animals to wood machines. To do the conversion would involve fitting a lay shaft in place of the motor then fitting external pulleys and a belt to reduce the speed. But that does not sort the blade guides, tension, workholding and the tyres.
 
If you want to cut much metal then a second hand imported metal cutting bandsaw with a bimetal blade could be a nice set up.  The imported bandsaws -for around £200 new- do have a few minor issues with build quality that are well known but once sorted they will cut  steel and ali without blinking. Would not be without mine.
 
There is some useful info on metal cutting bandsaws on www.starrett.com with a very good speed/ materials chart.
 
Regards,
Alan
Ian S C03/12/2010 10:26:35
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7468 forum posts
230 photos
The cheap ($NZ450) horizontal/vertical band saws are pretty ruggard we'v been using one for about 10yrs building agricultural machinery. Occasionaly it gets sworn at when it starts cutting of square,  but in general its OK, beats an 'armstrong' hacksaw.Ian S C 
Steve Garnett03/12/2010 11:29:59
837 forum posts
27 photos
Agree with all of the above when it comes to bandsaw mechanics. We have a really old Tauco (1940-something) which has been modified with external pulleys so that it's reduced about 4:1 from a 1400rpm motor, and it also has an internal gearbox to slow it further. So it's more or less as Ian described above. Yes we get some metal deposited on to the rubber tyres, but nothing that doesn't come off easily because these tyres are pretty hard, so it doesn't embed. You have to be pretty careful with blades though - use the wrong one on steel and it knackers it in no time. Normally for us it's not a problem because it is usually used on plastic, but it whips through non-ferrous stuff like there's no tomorrow.
 
We haven't tried bi-metal blades on it, and that may be a good idea. I will give it a go next time we order, I think.
Billy Mills03/12/2010 16:07:22
377 forum posts
Blades are quite a big subject! For cutting steel the bimetals are a bit more expensive but  last around 10 times as long, same as the equivalent hacksaw blades. The H/V metal bandsaw is a very good value tool, although not a thing of beauty it will not complain when you carve through 4" x2" ms bar or 3" round or 100 lengths of iron tube. It just does it. A new one in the UK is around £200 new.
 
It is also good with ali or steel sections. In the vertical mode it benifits from an additional table to enlarge the supplied job. It is then very useful for cutting out complex shapes, you can get the blade to act as a very narrow filling machine to nibble out waste. 
 
One of my favorite tricks is to mount a small drilling vise on a mdf block which is held in the bandsaw jaws for cutting small diameter stock or parts.
 
Another trick-If you grab a  block of mdf then screw a 2"x1" batten to the right side then clamp it in the vice, you can then saw cut part way through the batten. Place the stock against the batten then clamp it in place. The cut line shows exactly where the blade will cut so you can chop up short or long sections quickly. A stop block at the back ( or a g clamp) allows for mass production!
Steve Garnett03/12/2010 17:40:33
837 forum posts
27 photos
Yes, we have a few adaptations of a similar nature on ours for mass production purposes; you can do a heck of a lot pretty quickly with jigging on a bandsaw!
Clive Farrar04/12/2010 09:00:52
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125 forum posts
41 photos
Hi Robert,
                   I have had a look at our works machine and I see what you mean about the small pulley.  I was surprised to find that the drive pulley is just a single flat flange.
 
Using wonderfull excel the standard speeds check out and so with the standard drive pully the lowest speed I think you can get on this machine is 267 m / minute and that would be by building up the band drive flange to 320 mm OD , i.e. the same is the tyred band drive wheel. There is probably not that much adjustment on the motor mount.
 
To get to the speed you want from the standard motor pulley would need a 2 m diamater on the band drive flange.  err NO!
So if you turn that on its head you could look to make a smaller tyred drive wheel but to get down to 83 m /min would need the drive flange at 320mm  and the tyre drive band at 100 mm dia, which is too small the blade would fatigue too quickly.
 
So I would say you either have to reduce the motor speed or accept that you can not cut metal at your desired speed on this machine and take one of the alternative routes suggested.
 
regards Clive
Clive Farrar04/12/2010 09:01:40
avatar
125 forum posts
41 photos
Hi Robert,
                   I have had a look at our works machine and I see what you mean about the small pulley.  I was surprised to find that the drive pulley is just a single flat flange.
 
Using wonderfull excel the standard speeds check out and so with the standard drive pully the lowest speed I think you can get on this machine is 267 m / minute and that would be by building up the band drive flange to 320 mm OD , i.e. the same is the tyred band drive wheel. There is probably not that much adjustment on the motor mount.
 
To get to the speed you want from the standard motor pulley would need a 2 m diamater on the band drive flange.  err NO!
So if you turn that on its head you could look to make a smaller tyred drive wheel but to get down to 83 m /min would need the drive flange at 320mm  and the tyre drive band at 100 mm dia, which is too small the blade would fatigue too quickly.
 
So I would say you either have to reduce the motor speed or accept that you can not cut metal at your desired speed on this machine and take one of the alternative routes suggested.
 
regards Clive
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