SCM Minimax S45 Bandsaw Teardown & Overhaul

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Sideways

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Clean up continued today.

Acetone and a wire brush eventually dissolved the resin and got the lower guides apart.
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It helps to unbolt the two barrels from the carrier.
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When you reassemble, the thumbscrew with a flattened end is used to clamp the rear guide as this may need adjusting more often. A capscrew with a coned tip is used to secure the mounting bar which has a V groove to match and prevent rotation.
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The discs do indeed pull out of the plain bearings (probably oilite) once they're no longer gummed up with sawdust and resin.

When bolting the barrels back onto the frame, gently wind in the side guides until they touch and hold these square while you tighten up the capscrews. If you don't do this, it's possible for the guides to twist while you tighten up the bolts.
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The band wheels after wire brush to remove the sawdust. Good condition. Tyres still sound. Need just a few minutes with some scotchbrite and metalguard to remove the fine rust from the machined surfaces.
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Plated metalwork was cleaned with a brush, acetone as needed, and wiped over with metalguard for some extra protection. These parts are the fence, bracket and the support for the upped band wheel which is adjustable for tilt and height (tension).
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Sideways

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The table was also cleaned.
First scrape with a blade to remove resin, paint and rust, then medium or fine scotchbrite lubricated with wd40.
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Our preference is to do as little as possible to machine tables. We are not looking to interfere with flatness. A couple of rounds was enough, the first wipe down showed the stubborn rust spots and rings that needed some more attention.
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After cleaning, seal the surface with metalguard which must be left to evaporate off,
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then polish and do the same with machine wax. Any will do, but the liberon version contains anti rust additives and buffs to a nice hard, low friction finish after it has been left to dry.
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deema

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A quick shot of the underside of the table. These are good thick tables, and are nicely ribbed. SCM take the time to actual paint the underside properly. The mating surfaces to the quadrants for tilting the table are machines surfaces.


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deema

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The top wheel assembly is simple and rugged for what it does. There are two steel channels, made from very decent wall thickness steel that are held together by a rod that is secured by a circlip on either end. The shaft for the upper wheel is bolted to this arrangement.
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The two wheels are cast iron, and carry a flat tyre, rather than a crowned tyre. There are two bearings separated by a circlip at the back of each bearing. The bearings are pressed into the wheel hubs initially before being pressed into the shafts. This is one job where I believe it’s necessary to have a proper press, rather than ‘tapping’ the bearings onto the shafts.
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The lower wheel sits on a shaft that needs to be removed for both pressing it back into the wheel, and also when ever the belt is changed. This is the only part of the design I don’t like. The hub is pulled back into the body of the saw by a bolt and large washer. The shaft and hence the wheels alignment is made by adjusting 4 bolts around the circumference of the shaft at the 12, 3, 6 and 9 o’clock positions. To remove the shaft the easiest way is to take off the pull back bolt, and then mark the shaft orientation with respect to the 4 alignment bolts. I centre punched it at 12 oclock, I then slacken two of the 4 adjuster bolts. I do this so that when I put it back the chancers are by realigning the shaft and tightening up the two bolts it will need almost no adjustmen.
Shaft and pull back bolt / washer.
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The aligning bolts
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The inside where the lower shaft comes through
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Pressing the lower shaft back into the wheel
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Lower wheel put back, note, you have to fit the belt at this stage.
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Motor just poked back in and the belt out on both pulleys.
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deema

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The lower wheel hub back showing the aligning bolts tightened back up.
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The wheels are retained on the shaft by a M6 cap head screw and washer. We tend to chase most threads to be sure that they arnt full of foreign bodies.
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deema

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The blade guide assembly is again a well made unit. First of all the raise and lower gear is put back in. This is threaded and also (bad design) retained by a grub screw that impacts the threads. I ran a die down the M12 threads to allow the cig to run back on smoothly.
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An angle plate is bolted next to the guide, which has a spring that acts on a stud to push the guide hard against one side.
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The blade guards bolt on next. They are held by two fiddly cal head screws. You can’t fit this with the upper wheel installed…..ask me how I know!

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Jitter

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What a superb overall on the SCM you are both doing. Thanks both Deema and Sideways for such great work and detailed information about this bandsaw. I can’t thank you enough!

I am going to do your cast top cleaning methods on the Wadkin UOS, some great advice there and great pictures to show how it transforms.

A question I have-
Do you recommend releasing tension on the blade when it is not in use? (for this particular machine)

As a newbie to bandsaws and most other workshop machines, my questions will most likely be boring to the many knowledgeable people on the forum. I apologise in advance 🙂
 

Ttrees

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@deema
This is a most fascinating thread to see the in's and out's of a Centauro machine.
I've been looking into various designs of non shoudered bores in the last few weeks, and very thankful I can see an alternative way of doing things, should things not go to plan.

Could you tell me if that big skookum boss has some relief machined into it, so it only makes contact with the inner race, or if it's machined with a perfectly square shoulder.
No rush, yet to make some tooling to turn this on my wood lathe.
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deema

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Hi Ttrees, the boss on the spindle is larger than it needs to be as it only contacts the inner race of the bearing. I suspect the large size it to ensure it contacts the body of the machine with a good land area when pulled back.
I think the boss may well be a separate part that has been pressed onto the smaller diameter spindle. It had by eye a square face with no apparent radius at the inner intersection.

The wheels pressed into it, so without destroying the bearings, I can’t take a photo of the other side for you.
 

Ttrees

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No bother Deema, I was presuming this, and was going to aim for no bevel/chamfer first.
I have plenty spare old bearings from the machine to find out.
Likely it might take me a few tries anyway.

Thanks for taking the time to make this thread.
Tom
 

Sideways

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A question I have-
Do you recommend releasing tension on the blade when it is not in use? (for this particular machine)
I'm nearly as much a newbie as you are when it comes to bandsaws, I've overhauled a Startrite and a Kity before this, fettled, setup and used just a few more. So take this with a pinch of salt...

Unless it's a weak saw carrying the maximum width blade at full tension, I very much doubt that the frame of a bandsaw is bothered whether it's under tension or not. The S45 is a strong saw with a really good frame. Nothing to worry about there.

The possible benefits of releasing tension on the blade are taking pressure off
1. the bandsaw tyres
2. the top and bottom wheel bearings
from the blade sitting under tension in one position. This could conceivably encourage some sort of micro pitting on the ball races and certainly it could imprint on the tyres over time.

Depending on how much pressure is dialled in, there's an argument that a spring can lose it's tension over time. Metal behaves like elastic up to a point and I doubt that the spring is at any risk, but if you run a 20mm+ blade under high tension, then maybe there's something to consider.
Lastly, if creep and fatigue failure does happen to snap your bandsaw blade while it's sitting there tight but not being used, it makes a hell of a bang ! It might startle you into spilling your tea :)

If I had a saw that was in daily use, I'd take the tension off going into weekends or holidays. I wouldn't bother overnight but I'd not criticise anyone who did. They probably know better than me.
If I used a bandsaw occasionally as an amateur, I'd leave the tension off until I wanted to use it, and take the tension back off at the end of that day.

Experienced users, please come and set us both straight ....
 

TRITON

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You're making an excellent job of that. A big job, and doing all the parts is testimony to yourself and your skills. :cool:

My only niggle is you haven't painted it in some gaudy colour :LOL:
 

deema

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Not a hugely productive day today. The new owner asked for a mains cable 5m long…….and as is typical we had just 4m left……not a big deal, we had anticipated supplying a cable of circa 3m, so hadn’t ordered a new real. Rather than relying on the unreliable post we popped to the local electrical distributor to pick up some additional cable. We selected a particular type of cable for this saw, Sideways will explain the rational as he is in charge of the rewiring of the machine. We always replace all the cables in a machine, with age they become brittle and for us it’s a false economy for the new owner if it isn’t rewired throughout.
 

deema

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The tension in the blade is created by a draw bolt compressing a spring, pulling the wheel up. It’s a very simple and very effective way of doing it. Some saws have the spring below the wheel, and others above. Out of preference I prefer the spring above. The gauge for the tension on this saw is rather unusual, it’s a clear perspex cup, with markings on it indicating the correct position for the tension handle to be wound down to for different blade widths. The cup rotates to show different tension points. Simple and effective. However, the cup on this saw, when we relieved it of all the grime is actually crazed, it’s not broken, but somehow it’s crazed.

The photo shows the cleaned blade tensioning system after cleaning up installed. You can see how crazed the cup is making it difficult to see where the markings are. You can just make out the red markings of the tension setting.
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I took the whole assembly apart, the bits I’m showing are just for the cup.
The large circlip just provides a seat for the cup to sit upon. The Perspex tube just sits on top of the circlip and fits snuggly around the stem of the metal body (it sits around the fat end). It’s not a push fit, and you should be able to rotate it easily. This one was full of sawdust and was wedged on. I suspect saw dust got down between the perspex and metal body and with temperature changes caused the crazing as it slowly descended into the crack between the two.
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Well, that’s not good enough for us, we want the machines we restore to look and function as close to new as possible. I’ve ordered a new Perspec cup, an original table insert (as it was missing, we will make one ourselves, but it’s nice for the new owner to have an original) and a wheel brush from SCM spares in the UK. They have a minimum order value of £70 excluding VAT, and these items met that the criteria! The only downside is they won’t be delivered until early March. We will be delivering the machine before that and will send the new bits to him afterwards.
 

Sideways

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The saw is to be powered from a transwave 3ph converter and it is possible that it will be plugged in and out somewhat regularly if other machines share the Transwave.
This influenced the choice of a power cable.
If the saw was to be permanently wired in, or only occasionally moved, then SY flexible cable with a protective wire braid would be a good choice.
The downside of SY, is that it is rather stiff and unwieldy. An alternative is to use a high grade rubber flex. Code H07RNF identifies premium abrasion resistant rubber cables that are also oil and chemical resistant. These are excellent cables. More costly than SY and long lived.
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Sideways

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The saw has a simple pushbutton start switch and a latching off / emergency stop switch fitted in a box below the table.
The originals were in sound condition so were cleaned up and reused.
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The advantage of fitting controls in a sealed enclosure is dust resistance. Cable glands and a rubber seal around the box combine with industrial style switches which have rubber O rings around their mounting holes.
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The industrial switches are typical of the type. Made in three parts there is a button or switch up front, a mid section that secures the switch to the panel, and clip on blocks at the back that do the electrical switching. The contact blocks on these switches screw firmly to the metal section rather than using spring clips.

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Notice in the bottom image the contact blocks are labelled NO (normally open) green, and NC (normally closed) red. In most typical setups, the green contact block is clipped onto a green start button or rotary start switch. The red block onto a momentary stop switch or emergency stop button.

An important point to note. These switches operate a control circuit only. Power goes to the motor through a large 3 phase relay aka "contactor" that sits in a box on the back of the saw. The pushbuttons and the safety relay in the next post work at 3 phase mains voltage but carry only the small current that flows through the operating coil of the contactor.

FOOTNOTE: One small detail nagged at me and had to be put right after the event.
You may notice that the industrial switches in this control box have metal frames and bezels around the buttons. That is a nice quality detail, but used here in a plastic enclosure, an unlikely but hazardous fault could arise. IF a live wire were to come loose from one of the switches because of vibration, fatigue or a mistake in tightening the terminal screws, AND IF that loose wire happened to touch part of the metal clamp / frame on one of the switches, then that part and the metal bezel around the switch on the outside could become live at 240V.

Normally this would never happen because the enclosure would be metal and grounded. The frame and bezels of the switches make a good electrical contact with the box and are also grounded. In a plastic enclosure this can't happen. We needed to go back and explicitly earth the bodies of the switches as a safety measure against 3 pieces of bad luck coinciding.

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Sideways

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The next element of the wiring is the safety switch monitoring the upper and lower bandsaw wheel covers. When both doors are secured shut by a hinged bracket made for this purpose, a metal tongue or "actuator" is pushed into the slot in the red end. This closes the switch.
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Notice the simple box joint between the red and black parts of the switch. This can be separated and the red end rotated to point the actuator slot in 4 different directions to suit the application. A replacement switch might have the slot pointing the wrong way, but the red end is easily unscrewed and turned through 90 degree steps.

The safety switch is wired in series with the stop switch. Both of them have Normally Closed contacts and allow a small control current to flow while the motor is running. If the tongue is pulled out of the safety switch it acts exactly like pushing the stop button and the power to the motor is cut.

The safety switch is an Italian one, available from a few sources if a spare is needed.
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This image shows there are actually two switches inside for versatility, a NO and a NC.
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We use only the contacts that are Closed when the actuator is inserted.
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The safety switch is bolted to the chassis just above the on off switches and is connected into the circuit inside the on off box.
 
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Sideways

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@TRITON, that comes when he asks me what colour I want it, as he's kindly giving it to me, aren't you Deema (please!) ?;);)
Is it just me ? I really like those big Otto Martin panel saws with the graffiti paintjobs.....
No, not volunteering. If I tried it would look like a 3yr old did it !
 

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