Asian 4x6 Band Saw V belt sizing

[superc]

I have a decades old ShopForce brand 4x6 bandsaw.  After several decades of happy use it began giving me problems such as the blade not cutting, etc., then the belt finally reached the end of it's stretch and came apart.

I wish to share my findings.  First, it does NOT use a 1/2" belt.  Use of a 1/2 inch wide replacement belt produces wildly high excessive blade speeds.  Instead the saw pulley uses a 10mmx8MM or 3/8" belt.  This size of Metric belt is called an SPZ class belt.  Your original belt may, or may not, have a 3 digit number on it.  Mine had a 559.  That is about 22".  559 560 and 562 are all available SPZ belt sizes.  Since the pulley arrangement has a lot of play in the adjustment range any of those should work in your machine assuming you too have one of the older metric belt arrangements.  I suspect the American 3/8 x 22" size belt would probably also work in my machine.

Be dubious when you read someone else just threw in a 1/2" belt of some kind or another and everything has been just fine since then.  Tell them to check their blade speed.   

[tom osselton]

If its turning faster wouldn't that be the proper speed as opposed to a worn belt slipping?

[Manxmodder]

Irrespective of how much further out the 1/2" belt sits on the pulleys I think the ratio between driver and driven remains the same so the blade speed would still be as intended.

Or am I missing something here?.....OZ.

[philf]

Irrespective of how much further out the 1/2" belt sits on the pulleys I think the ratio between driver and driven remains the same so the blade speed would still be as intended.

Or am I missing something here?.....OZ.

Hi OZ,

I'm being a bit pedantic by saying that you are missing something but the difference probably doesn't matter too much.

If you section a vee belt there are tension fibres set below the top (wide) surface of the belt. This usually corresponds with a position inside the vee groove and sets the effective (or pitch) diameter of the pulley. If you use a larger section belt then this will move the pitch line out of the groove and will increase the effective diameter.

E.g. If you have 2" and 4" pulleys (ratio 1:2 or 50%) and you fit a bigger belt you may increase the effective diameter by 0.25" to 2.25" and 4.25" (the ratio then becomes 53%).  Not a huge difference but a difference nonetheless.



Cheers.

Phil.

[Manxmodder]

superc,is your saw the same shopforce model as this one in the photos I've linked below?

The blade speeds are printed on the motor and it would be easy to check  your actual blade speed against the specified speeds by putting a temporary  paint or chalk mark on the blade and counting how many times it goes past one of the rollers in one minute.

The number of revolutions you observe in one minute multiplied by your blade length in feet will give you a fairly accurate figure for your actual feet per minute to compare with the blade speed and see if it is running within the speeds specified by the manufacturer.....OZ.

http://auction.ridofstuff.com/details.cfm?ID=1326490#photos

[superc]

Yep that's the model.  Uses 10mm belts.

Gentlemen.
My statement was, "use of a 1/2 inch wide replacement belt produces wildly high excessive blade speeds."

There exists a reason I chose those specific words.  I measured the speed that resulted with a 1/2 inch belt and the pulleys configured for a blade speed of 80 feet per minute.  Precisely, with a Jaquets Indicator.  Then I double checked pulley setting and also the Jaquets against a known standard (a tractor PTO) and yeah it works just fine.  Then I took a reading of the blade's speed again, and again. 



I stand by my use of the words wildly excessive.

Average feet per minute speed of the blade with a 1/2 inch belt was about 1,100 fpm.

In the 6 seconds allotted the  small wheel spins and passes the 300 inch mark not less than 7 times.

[DaveH]

I have a similar 4x6 band saw and my belt is metric 13 x 560 A590 A22.

My saw is set on fastest 200 ft/min - which means by your reckoning my blade speed would be about 2750 ft/min. I can say without measuring it it doesn't run any where near that speed.

I find it hard to believe that the speed can go from 80ft/min to 1100ft/min with just a small increase in belt size. Something just isn't quite right.
 
DaveH

 

[Manxmodder]

superc,I agree with David,there has to be some error here somewhere because those readings are massively over what would be seen by fitting a 1/2" belt to a 3/8" pulley.....OZ.

[superc]

Is 'massively over' the same as 'wildly excessive'?  I think so.

Philf is on the correct path, but his numbers are too small.

The big pulley's (bottom) central shaft (which a 10mm belt rests against) is 43mm in diameter.  However, because it is too wide to properly enter the pulley, a 1/2" belt sits around the pulley at 59mm.  The other pulley has a shaft of 48mm diameter which a 10mm belt reaches, but the 1/2" belt never gets closer than 60mm to the shaft.

[philf]

  Precisely, with a Jaquets Indicator.  Then I double checked pulley setting and also the Jaquets against a known standard (a tractor PTO) and yeah it works just fine.  Then I took a reading of the blade's speed again, and again. 

In the 6 seconds allotted the  small wheel spins and passes the 300 inch mark not less than 7 times.

Hi Superc,

I agree with Dave H and Manxmodder.

I haven't any experience of the Jacquet instrument.

You can usually see the welded area of the blade so why not just time how long it takes the blade to a full pass.

The 4x6 bandsaws use a 64.5" blade. At 80 feet per minute the blade would take about 4 seconds to do a complete lap.

For 1100 feet per minute the blade would be doing a full lap in 0.3 sec!

Something just doesn't add up.

Cheers,

Phil.

[superc]

I am also noting with great amusement a total lack of standardization from machine to machine on pulley belt size regarding the Chinese 4x6 saws. 

DaveH has a 13mm 560 A22 whereas my own is a 10mm 559 A22.  Both 559, 560 and even 562 (which another user has quoted to me as the markings on his own belt) are close enough as metric sizes, when speaking of spring loaded pulley arrangements, to 22" for 22" to be the operative belt length dimension. 

Of greater significance here is that another user is reporting his original belt is an actual 1/2"x22" size. 

Where this will kick in is if you ever decide to buy one of the spare pulley things for sale on Ebay.  Clearly different sizes are out there and we should be sure which one we have before randomly putting them inside our machines.

[superc]

Philf,

A full lap in about 0.3 seconds.  Yeah I'd say that's just about right and what I see.

Actually that does add up very nicely and your calculation is completely explaining why I am getting at least 7+ rotations of the 300 inch mark in 6 seconds.  In short both your rough calculation and the Jaquet indicator agree..  300 in. / 64.5 = 4.65 blade lengths to one revolution of the 300 inch pointer.  7 revolutions in 6 seconds mean 2,100 inches.  For linear foot per minute readings with the Jaquet,  /2 = 1050, now add 1/2 of the big pointer's number.  Voila 1,100 fpm.

[lordedmond]

May I ask a stupid question but is this saw a wood saw because that's the belt speed I would expect to find ?
Stuart

[superc]

They are supposed to be metal saws with a blade speed as shown in the photos provided by Manx Modder (i.e., 80, 120, 180 fpm), however wood blades of the proper size do exist and I (using those) have cut boards with it very nicely. 

[DaveH]

They are supposed to be metal saws with a blade speed as shown in the photos provided by Manx Modder (i.e., 80, 120, 180 fpm),

The plate on my machine say's 80, 120, 200. 

 
DaveH

[PekkaNF]

What about 50/60 Hz difference?

I should check the speeds on my metric machine and see how they compare.

Pekka

[superc]

DaveH, that's a good point and further evidence of the variation in these things.  The speed numbers I wrote above are from the photos linked to by ManxModder.  The sticker on the motor of my own is also 80, 120, 180.

For those not familiar with Jaquets Indicators, these things are early manual tachometers designed specifically for the purpose of checking and adjusting the speed of spindles, conveyor belts, cog wheels, saws and the like in factories or in the field when making repairs (say on a combine or a tractor's PTO).  They are very accurate.  Electricity and changes in technolgy has led to them pretty much being replaced by cheap electronic laser readers, but the hand held mechanical things can still be special ordered although I note with some bemusement the newer ones work in meters rather than inches, feet or yards.  My understanding is Jaquet started marketing them through HH Sticht sometime around 1910 but by 1990 switched manufacturing emphasis to cheaper plastic and laser readers.  Multiple versions exist, some with faceplates set up to show RPMs, some with faceplates set up to show inches or linear feet per minute, some with hi-lo ranges, some (like mine) that don't care, some with both the RPM  and the linear feet per minute reading shown plainly on the dial, some with a built in 3 second chronometer, some with a built in 6 second chronometer.  You select one kind of probe for pressing against the central axis of a shaft or a spindle to get an RPM, or a wheel of the appropriate size for getting a linear reading.  Both HH Sticht and Jaquet are still in business.

http://www.vijaytradesyndicate.com/index.php/textile-instruments/jaquet-swiss-make-mechanical-tachometer

[Manxmodder]

superc,can you check your motor for spindle rpm with that mechanical tacho.

Let us know what reading you get....OZ.

[superc]

Okay.  Did so.  Interesting.  Must be a two pole motor.  This is probably pushing the upper limits of my 60 - 90 year old tachometer or at least the upper limits of my ability to count how many revolutions of the small hand in six seconds.  The first time I blinked and missed some RPMs, so no more fast stuff.  Comes out with no load on the pulleys at about 3800 RPM.

[Manxmodder]

Interesting,as the specification plate on the shopforce motor in the link I provided earlier shows a photo giving the motor speed as 1700rpm,which is about what I would have expected,and would be roughly the same as the rpm on my 6x4 saw.Link reproduced again for convenience.
http://auction.ridofstuff.com/details.cfm?ID=1326490#photos

Maybe you could also check how many revs of the of input/driven belt pulley are needed to produce one full turn of the driven saw blade wheel....OZ.

[DaveH]

I decided to have a little 'chat' to my bandsaw. I wanted the saw blade to go at about 1000 ft/min, it looked at me for a couple of seconds and then fell over laughing on the floor.   
 
DaveH

[Pete W.]

SNIP

The big pulley's (bottom) central shaft (which a 10mm belt rests against) is 43mm in diameter. 

SNIP

Also, I might have misunderstood this but surely a Vee-belt is supposed to contact only the sloping flanks of the pulleys - it shouldn't touch the bottom of the groove.

I can't remember where I read it (somewhere on Mad Modders) but I seem to remember someone complaining that his bandsaw had been assembled with the reduction gearbox reversed - that would give rise to excessive speed. 

[mattinker]

I suspect that someone substituted a higher RPM motor at some stage, maybe to use it to cut wood. These 4X6 bandesaws run 1700 rpm motors in the us on 60hertz AC current and 1500 RPM on 50herts European installations.

The difference between a 1/2" and the original 10mm belt would not give the huge speed differences encountered.

Regards, Matthew

[philf]

superc,

I've just had a look at my saw (made by Clarke) and with a 50Hz 1,420rpm motor the three speeds given in the manual are 65, 95 & 165 ft/min. I checked the blade speed on the 65 ft/min setting with a Deumo mechanical tachometer and it's correct to within 1 ft/min.

Even with 3,800 rpm motor output this would only give 174, 254 & 441 ft/min. (By the way - 3,800 rpm doesn't sound right for an induction motor.)

Assuming your gearbox has the same ratio as everyone else's then I'm stumped. 

As Stuart pointed out 1,110 ft/min might be OK for wood but for sawing even aluminium with a HSS blade it's many times too fast.

Phil.

[Manxmodder]

SNIP

The big pulley's (bottom) central shaft (which a 10mm belt rests against) is 43mm in diameter. 

SNIP

Also, I might have misunderstood this but surely a Vee-belt is supposed to contact only the sloping flanks of the pulleys - it shouldn't touch the bottom of the groove.

I can't remember where I read it (somewhere on Mad Modders) but I seem to remember someone complaining that his bandsaw had been assembled with the reduction gearbox reversed - that would give rise to excessive speed.

Hi there Pete,the reduction box on these saws is of the worm and wheel type so I can't imagine how that setup can be assembled to give any higher ratio,unlike if it was a pair of toothed gears.

You are absolutely correct in saying that a V belt shouldn't be contacting the well or bottom of the pulley,the angled faces of the belt should only be in contact with the angled faces of the sheave or pulley ...OZ.

[Manxmodder]

superc,

I've just had a look at my saw (made by Clarke) and with a 50Hz 1,420rpm motor the three speeds given in the manual are 65, 95 & 165 ft/min. I checked the blade speed on the 65 ft/min setting with a Deumo mechanical tachometer and it's correct to within 1 ft/min.

Even with 3,800 rpm motor output this would only give 174, 254 & 441 ft/min. (By the way - 3,800 rpm doesn't sound right for an induction motor.)

Assuming your gearbox has the same ratio as everyone else's then I'm stumped. 

As Stuart pointed out 1,110 ft/min might be OK for wood but for sawing even aluminium with a HSS blade it's many times too fast.

Phil.

Phil,I have the Axminster swivel head version saw,on which the 560 watt motor runs at 1720 rpm at 50hz.

The blade speeds are given as 23, 34 & 54 m/min.

Regarding speed ranges of these type of motors,as you say, 3800 rpm does sound extremely high, even if the motor was of the 2 pole type(normally around the2700- 3000rpm mark)....OZ.

[lordedmond]

Evan at 60hz a two pole or as I refer it's a single pair of poles

At its best it would be 3600 rpm with no slip synchronous running ,at normal slip it would be about 3550 rpm

I would guess some tyke has replaced the motor

The whole belt speed does not add up for a metal cutting band saw , but and it's a big one it may have been like it from new we all know the QC

Stuart

[superc]

Nah, the 1/2 inch belt definitely kicked up the speed.  Looking forward to the arrival of a belt the same size as the original.  Let''s see what happens.

LoL to motor specs.  The glued on paper Shop Force left on mine says a 1/2 hp, OR a 3/4 HP may be used.  No spec plate exists on the motor casing.

A quick google for AC motors shows many types fit the 1/2 or 3/4 "spec."  Which type they stuck on it is anyone's guess.