SCM Minimax S45 Bandsaw Teardown & Overhaul

[Ttrees]

@deema
I agree with your comment on the flat tires, concerning them providing better tracking....
if you mean whilst "dynamic testing" (Kelly Mehler has mentioned that term aptly named term on a tablesaw video, I think it's good way of putting it)

So if you are referring to tracking whilst the machine is cutting, then most folks running larger Italian machines with flat tires agree, especially the folks using euro guides, and not ceramic ones,
Statements like the machine cutting as fast as one can feed the material through it,
without the blade walking back and rubbing against the thrust guides, leads me to think so.

After dressing my real rubber vulcanized tires, it seems to have even more grip on the blade than before, although yet to be 100% on that. (Too many variables for science)

I have asked about the grip differences regarding actual rubber, and the composite rubbery compound which is on replaceable tires, but haven't found much talk about it,
not to mention adding urethane tires to the equation, a bit odd!

I've not come across anyone who actually tracks a narrow band off, or close to the set being off the wheels.
There is a lot of talk about tires/tyres on the web, but not many folks actually dress the tires, which is odd, as I'm guessing not everyone who has flat tires or near flat tires
uses a resaw blade only.

Plenty of evidence out there, suggesting that this makes sense to me.
A tell tale sign is folks running only narrow blades on these machines,
because the front of the tires, acting much the same as a pronounced camber
is too worn for the wider blade to track well.

I've looked into this as I have more unanswered questions about flat tires, to do with the possible importance of the edge of the rubber.
(a non concern regarding even a tiny camber)

To cut to the chase, I reckon along with most, agree its worth evening the wear out as much as possible,
say if ones tires were somewhat old and a bit soft, but still OK, are likely more prone to wear.
Not having experienced that from the one narrow very very fine blade I have,
which hasn't had much use,
but can see what a 3/4" blade does to a dressed tire, so this occurrence likely exists to some extent, and good practice to keep an eye on things periodically,
as I'm guessing all tires aren't created equal.
Even the two vulcanized tires on my machine differs in hardness, so checking wear on both suggests to me to be good practice.

The Centauro/minimax being the machines which are talked about on the American forums, as not too many in the UK seem to be seeking to do the best resawing possible, and regard the bandsaw as more of a jack of all trades tool.

I reckon there would be a lot more than vague(ish) talk about tires if Centauro didn't have that quick change system which Sam Blasco demonstrates on the MInimax MM16.

Perhaps we would have a better answer whether wear occurs with small blades and various rubber compounds and such.
Not very interesting to the folks who can swap them out in a few minutes.
Some interesting comments I've read before, about NOT putting this type of "rubber" in very hot water beforehand!


Sorry for mucking up your thread with my ramblings.
Thanks for taking the time to show why these machines are a cut above the rest.

Cheers
Tom

 

[Sideways]

Thanks for the link to Berger. They have a great range of stuff.
Springs are proving interesting to investigate. we'll figure this out and write it up, but the starting point is :
We need a spring with a 10mm or greater bore to fit the adjusting screw that goes down the middle.
Unless we modify something, we need a spring with a 20mm or less outside diameter because the spring drops into a tube.
We have a target length of 65mm but can use a longer spring if that's better. Longer may inded be better in some regards but any change from 65mm would be at the expense of the tension scale on the new perspex collar we've just ordered which is calibrated against a 65mm spring (ho hum).
Sources of advice say that it's better not to compress a spring to the point where the coils bottom out (all turns touching) as this does reduce the life of the spring (at least when you are putting it through thousands of cycles of compression and release.
But fully compressing a spring is a way to limit the amount of tension that can be applied and so it acts as a designed in limit to prevent overstressing the frame. A new spring is far cheaper than a new frame. I can see why SCM may have designed this as they did.

Figures in the range of 15,000 to 20,00 to 25,000 pounds per square inch are given by vendors as recommended tensions for carbon steel blades. Higher for bimetal and special steels. We're asking some questions to confirm these, then we'll convert them to a tension for the heaviest blade that the S45 can safely run, and that in turn into the max tension needed from the spring. That will be interesting.

Once we know what force we require from the spring, we can start looking through the options that fit.

 

[Ttrees]

Sorry to keep butting in, but as a self professed bandsaw fanatic, I can't resist, as it makes for very interesting reading!
"Just" incase you guys haven't seen this thread before.

https://www.swedishwoodworking.com/...e-tension-spring-on-the-hammer-n4400-bandsaw/

 

[FlatlandsF7a]

Thanks for the link to Berger. They have a great range of stuff.
Springs are proving interesting to investigate. we'll figure this out and write it up, but the starting point is :
We need a spring with a 10mm or greater bore to fit the adjusting screw that goes down the middle.
Unless we modify something, we need a spring with a 20mm or less outside diameter because the spring drops into a tube.
We have a target length of 65mm but can use a longer spring if that's better. Longer may inded be better in some regards but any change from 65mm would be at the expense of the tension scale on the new perspex collar we've just ordered which is calibrated against a 65mm spring (ho hum).
Sources of advice say that it's better not to compress a spring to the point where the coils bottom out (all turns touching) as this does reduce the life of the spring (at least when you are putting it through thousands of cycles of compression and release.
But fully compressing a spring is a way to limit the amount of tension that can be applied and so it acts as a designed in limit to prevent overstressing the frame. A new spring is far cheaper than a new frame. I can see why SCM may have designed this as they did.

Figures in the range of 15,000 to 20,00 to 25,000 pounds per square inch are given by vendors as recommended tensions for carbon steel blades. Higher for bimetal and special steels. We're asking some questions to confirm these, then we'll convert them to a tension for the heaviest blade that the S45 can safely run, and that in turn into the max tension needed from the spring. That will be interesting.

Once we know what force we require from the spring, we can start looking through the options that fit.

Ah yes, your outside diameter is limited to 20mm because of the indicator gauge cup. My saw doesn't have one of those, so the spring sits 'through' the frame, and the bore of that hole is 30mm (if memory serves) allowing me to use the 25mm spring.

 

[Sideways]

Sorry to keep butting in, but as a self professed bandsaw fanatic, I can't resist, as it makes for very interesting reading!
"Just" incase you guys haven't seen this thread before.

https://www.swedishwoodworking.com/...e-tension-spring-on-the-hammer-n4400-bandsaw/

It's a good article. As it happens, yes, I had read and bookmarked it some time ago. Thanks for the reminder
Tuffsaws continue to earn their good reputation and are being extremely helpful with data about their carbon and M42 steel blades. Once we've have all the numbers we need, we'll add the calculations and conclusions here

 

[FlatlandsF7a]

@FlatlandsF7a thank you so much for the measurement, I think you have a different generation of saw to the one we are working on if it doesn’t have a rack. I wasn’t aware they did a variant without a rack. Do you have a picture / serial number of the machine and I will see if I have a parts list for it.

There are two reasons we think it’s taken a set, firstly the saw is rated for standard blades between 6 and 20mm, and the spring when not compressed at all is just a smidge above the line indicating correct tension in a 6mm blade. Secondly, I think the clear acrylic pot has crazed due to the adjuster handle having been screwed down so far it’s actually compressed the pot. A sign they couldn’t get the tension high enough. (Although some blade materials, ie M42 need a higher tension, so a saw that takes a 20mm standard blade may not be able to fully tension a 20mm tougher material blade.) We are going to make a spacer to stop this ever happening again and also replace the threaded bar on the adjuster to make it longer to a accommodate the spacer.


If anyone else with a S45 could also measure their spring that would be really brilliant. If all three are the same / similar, we know it’s good.

Was just in the shed and snapped these pictures of the blade guard assembly. Pretty difficult to get clear pictures, but perhaps it will be enough. I forgot to look for a serial number on the machine, but will edit this post when I get one!

 

[Fergie 307]

Interesting about the belts. When you overhaul an old imperial machine and fit a modern motor made to IEC / metric standards, one or both pulleys may need changing and belts usually do because the new motor has different dimensions. It is quite tricky judging the correct belt length from measurements even when you understand how belts are sized.
In this case, the motor is already IEC and in good condition. No need to change. The starting point was to fit a new belt the same size as the one taken off. Even the most straightforward swap can be tricksy.
Here you can see the range of adjustment available in the (original and unchanged) motor mounts for tensioning the belt. There's about 1 inch vertical movement in the slots of the four bolts. So the belt needs to be pretty close. With the A38 belt, the mounts are about the middle of the slot, rather than being over tight at the downward limit of the holes with an A37.

View attachment 128481
The motor is held by the four 4 bolts through a flange. The bolts are loosened, and the motor dropped to fit the belt. The lower band wheel is removed for a belt change as the belt is too small to be stretched over the wheel while it's in position. Once the belt is sitting in the grooves of the motor pulley and lower wheel, the wheel is refitted to it's spindle and the motor lifted by a jacking bolt until the belt is comfortably tight. About 1/2" sideways movement when you push firmly but not hard on the belt midway between pulleys is about right.

View attachment 128482

Looking great. From earlier pictures looks like you have a solid v belt. Might be worth considering a notched type, they grip better so you can get away with less tension. Bit late I know as you already have the new one, but for similar projects well worth a try.

 

[deema]

Sideways and I have spent some time reading up about springs and doing the calculations. Now, neither of us would claim to now know a lot about springs, but we know a lot more than we did!
So, I’m summary, compression springs should not be compressed so that the coils touch each other, in fact they typically should not be compressed more than 25% of their relaxed state. Each spring has a slightly maximum compression limit, which is stated in the specification. Good design would incorporate some form of bump stops to or event the spring being over compressed.

Ian at Tuffsaws has been extremely helpful and provided us with a lot of data on blades, we are eternally grateful to him for his help and assistance. I run Tuffsaws blades in my own bandsaw, and have always been extremely pleased with the blades and delighted by their customer service. We always recommend them to the new owners of any bandsaw we sell or service. In reality, the saw is only as good as the blade you put into it.

 

[Sideways]

Looking great. From earlier pictures looks like you have a solid v belt. Might be worth considering a notched type, they grip better so you can get away with less tension. Bit late I know as you already have the new one, but for similar projects well worth a try.

Spot on with your advice there.
There is a future thread in the pipeline when I finish my Fobco 7-Eight drill.
There's a notched belt hanging on that waiting to be fitted
I think of notched belts as especially useful if you need the belt to go around a small diameter pulley, but they work as an upgrade to most machines.

 

[deema]

Sideways and I have backward engineered the tensioning arrangement for the saw, it’s the first time we have done this, so although we believe our maths and assumptions are correct if anyone knows better / spots an error in our thinking please pitch in.

First off, we wanted to get a good idea of what the spring constant should be for the existing spring. We could measure it, but we know the spring has gone beyond its yield point, as it’s shorter than it should be. Therefore, any constant we measure may not be correct as the elastic slope may be different as well as shifted due to none elastic stretch. I will highlight that neither of us are mechanical engineers, we are both electronic engineers, I have spent most of my working like running mechanical engineering company’s for my sins. So, a long winded way of saying that I think I know enough to be dangerous with mechanical stuff

To help with the explanation, there are two important points when stretching a material, the first is the point at which a material won’t return to its original length after being stretched. This is called the yield point. Below this, the material is elastic, it will stretch and not take a set. Beyond the yield point the material stretches and will permanently remain stretched. However, it hasn’t broken. This area is none elastic and none linear, if you keep stretching the material it will eventually break, the peak force it can withstand before it breaks is the ultimate tensile strength of the material, which is higher than the force needed to break it.

The spring must be designed to operate in its elastic region, so, it’s compression is proportional to the force it generates. As way of explanation, if it takes 100kg to compress the spring 1mm it will take 200kg to compress it 2mm and so on up to the yield point. We used this to work out the spring constant. A springs equation is Force = spring constant x change in springs length.

We measured separation f the graduations on the clear plastic cut, which indicated how compressed the spring should be for each width of blade. The results were

We know the spring should be 65mm long, so by measuring how long the spring would be at each graduation we could work out the amount by which it was compressed. As a check, we calculated the linear spacing to verify our measurements were accurate. It isn’t easy to measure as the lines in the cup are fairly think. We found that our measurements were very good and had good correlation to the theoretical values.

We now had the amount by which the sping was compressed. One part of the equation.

 

[deema]

We needed to know what force the spring needed to exert on each blade width to work out the contact by rearranging the equation. Tuffsaws came to the rescue, and Ian provided us with support, help and data to work out the next bit. A big thank you to Ian.
We decided to look at the thinnest blade and widest blade the saw can take, which covers the range of tensions the spring has to work over. The SCM S45 specification is that it takes anything between 6mm and 20mm wide blades. We also wanted to cover the range of materials Tuffsaws provide for blades. From standard carbon steel blades to the more expensive but far longer lasting M42 which is what I use on my own bandsaw.

Tuffsaws web site can be found at

https://www.tuffsaws.co.uk/
I hope Ian doesn’t mind a quick snap shot from his web site of the M42 blade characteristics. I’m sure with the benefits they bring that the new owner who cuts a lot of oak will be using these blades and we want to ensure the saw can tension them up.

Ian’s blades need different tensions depending on the material they are made out of. This is something that should be considered when tensioning a blade on a bandsaw, the markings will be ‘a rough’ guide as the manufacturer will have assumed a particular blade material and also tooth design. So, for Tuffsaws blades:

We have stated the data in both PSI and N/mm2, it’s the same just different units of measurement, and you will come across both when looking at saw data. The pressures are defined by how much pressure is being exerted over a square inch (PSI) and over a square MM (N/mm2). The same pressure is required for every blade of that material. So, a 6mm wide blade and a 20mm wide blade need the same pressure to tension them. However, they are different sizes, so initially it would seem from the data that you just need one pressure for each blade material irrespective of the blade width. This is where the area comes into consideration. To work out the force needed to apply the same pressure in the different blade widths we need to know the cross sectional area of the different blade widths. A 6mm bkade will have a smaller cross sectional area than a 20mm blade.

 

[deema]

Bandsaw blades can be bought in numerous teeth per inch configurations, each designed for specific cutting jobs. We are only interested in wood cutting and not metals for this saw. The blades thickness varies and increases as the width of the blade increases. Ian’s blades use typical thicknesses that are found within the industry. The 6mm blade is the thinnest and the 20mm blade is the thickest material. We also need to consider how much material is taken out of the blade to create the teeth. This effectively reduces the cross sectional area. Again, Ian helped with tooth depth data and I measured a couple of blades. So for the two extremes of blade the cross sectional area is

If you multiply the PSI or N/mm2 constant of each material size by the cross section of each blade you end up with the force required to tension the blade. I used the N/mm2 so the tension is expressed in Newtons.

The bandsaw is a continuous loop, so the sling is pulling against a loop, or effectively two blades, so the actual force the spring needs to exert is twice that which is calculated for a single blade. In other words is the about calculation times 2. You therefore end up with: (I used N/mm2 so the result is in Newtons. If you want it in KG divide by 9.81, or 10 for a rough estimate)

 

[deema]

We can now work out what the spring constant is likely to be using the tensioning scale on the machine as we have all the data we need. Rearranging the equation, Spring Constant (K) = Force (F) / extension. So for the 6mm and 20mm in Carbon steel we get
K = 835 / 5 = 167. (6mm)
K = 2400/ 11.7 = 205. (20mm)

K is not the same due to the tooth geometry, and is gives a range of what K can be. This is why the exact marks on the bandsaw tension gauge are just an indicator.

Looking at M42 the constant K needs to be to
K = 1236/ 5. = 247. (6mm)
K = 4900/ 11.7. = 419. (20mm)

So we can see that the M42 needs a much larger force to tension it and to use the scale of this saw for the material would give a terrible tension. Usually Ian would recommend a narrower blade when selecting a M42 due to the likely hood that the saws not capable of fully tensioning it.

We come back to the yield point, which now becomes relevant. Springs of this power must not be compressed beyond a certain limit, certainly not so the coils touch each other. Of the spring is over compressed it won’t have the same spring constant and probably be shorter. So, a good design would incorporate some mechanical means of limiting the travel. This saw doesn’t have one, and I. Fact I have yet to see a bandsaw with a bump stop for the spring. We will for this saw hopefully incorporate one to more ent the sling being overly compressed.

The M42 needs the spring to exert 4900 N of force to properly tension the blade. To out it roughly into KG which is easier to think about, it’s 490 KG or about 1/2 tonne. That’s a lot of pressure in the spring, and also the saw frame must be able to withstand it without exceeding its elastic limit. The frame will flex, but after the tension has been released should return to its normal position. If it flexed too much the geometry of the wheels will be interrupted and the saw not cut well, the frame will become part of the spring. This is why it’s important to loom for a bandsaw that has a very strong frame. Well designed and thick walled components. Cheap bandsaws use thinner materials and flex too much / can’t properly tension up the blades they are supposed to take. Sideways and I may comment about this again……hope your not getting too bored!

 

[deema]

Springs to have a long life and also to not go beyond their yield point should be compressed in their working range as little as possible. Typically springs should not be compressed more than 25% of their length. It’s far better to be around 15% of the length. For a user, it would also be nice to have a scale which is as long as possible to make reading / adjusting easier. The scale on the SCM is very small, especially as you can see the forces that are being applied. However, if we use the typical spring design guides we can work out what the ideal length of spring should be for the scale.

The total compression of the spring on the scale is 11.7mm, so the ideal spring length would be no shorter than 78mm at 15% compression. For the spring used the actual percentage is 11.7/65. X 100 or 18%. So not a bad design.

Most badsaws are designed for use with carbon steel blades, so the spring constant will be some where around 200.,I’ve actually asked SCM technical what it is, and what the maximum compression is so that we could design the bump stop properly if we don’t change the design.

What we can say with a high degree of confidence is that the existing spring cannot fully tension a 20mm M42 blade (which is why Ian at Tuffsaws if ordering a M42 blade will advise a blade narrower than your saws capacity).

Sideways and I have been playing around with improvements to the design of the tensioning system for this saw. We would like to use longer springs to reduce the fatigue, a bigger scale, and one that can accommodate a 20mm M42 blade. We also want to reduce the friction in the mechanism to make it easier to adjust. We will on Monday be ordering the parts needed, and will document how successful we are.

 

[Sideways]

And cheers FlatlandsF7a - the spring tables at Berger tools have been really useful to understand what forces and spring rates are achievable with a readily available range of springs.

 

[Andrewy]

Hello, interested to read this. I have a 2019 sc45 n. I found the thread while looking for information on setup of the lower wheel (a 1" blade sits with the gullet at the edge of the top wheel, but overhanging the bottom by 3/8) will check planarity etc.

My tension spring is 63mm.

 

[Sideways]

Hi Andrew. How do you find the 25mm blade runs ?
I ask because the older version we are working on is only specified for blades between 6 and 20mm max. At 25mm I'd expect you to have problems tensioning it fully.
Do you have a manual for your s45n ?

 

[Andrewy]

Hi, it seems to run pretty well. I had some tracking problems when I first got/tried the saw.. using the blade which came with it. I did the usual recommended thing and bought some blades from tuffsaws. Using the 1" blade I was able to resaw some 280mm (apologies for going metric) sycamore, much easier/better than I had dared to hope. Currently running well in that sense. Sticky lower guide bearing, stiff depth of cut adjustment and the lower wheel blade overhang are my only concerns. I was able to get a pdf manual from the service/parts outlet in uk.

 

[mindthatwhatouch]

Hi,
What a great thread, looking forward to the blade tensioning update as never been happy with mine. Not wishing to hijack your thread but would appreciate your thoughts on the below. (If you want me to move it to a new thread, just say so)

Single phase machine. I got it running (came with electrical motor issues) believe it or not cleaned it up a bit and may have changed the wheel bearings, honestly can't remember. With the view to using it and improving it when I get round to it.

Main issues are Bottom guides.
approx 50mm to the underside of the table. options on changing the cool blocks type set up. (yes, those bits of wood are the same ones that it came with about 4 years ago)

Woeful dust extraction.
previous owner has cut a hole near the top of the lower cabinet, this is boxed in internally with a slot for the blade but I still get a lot of dust falling to the lower outlet at the base of the saw and this gets dragged to the top cabinet.

 

[FlatlandsF7a]

Hi,
What a great thread, looking forward to the blade tensioning update as never been happy with mine. Not wishing to hijack your thread but would appreciate your thoughts on the below. (If you want me to move it to a new thread, just say so)

Single phase machine. I got it running (came with electrical motor issues) believe it or not cleaned it up a bit and may have changed the wheel bearings, honestly can't remember. With the view to using it and improving it when I get round to it.

Main issues are Bottom guides.
approx 50mm to the underside of the table. options on changing the cool blocks type set up. (yes, those bits of wood are the same ones that it came with about 4 years ago)


View attachment 128932
View attachment 128933



Woeful dust extraction.
previous owner has cut a hole near the top of the lower cabinet, this is boxed in internally with a slot for the blade but I still get a lot of dust falling to the lower outlet at the base of the saw and this gets dragged to the top cabinet.

View attachment 128934

This looks a lot like (a slightly more hard-lived version of) mine, although mine has a manufacturer included dust extraction port at that point. I am also curious about installing different guides under the table, as mine has the same very small clearance.