Band saw arm weight

I have had a Clarke CBS45MD 4 1/2 inch band saw for a few years now and it is a fabulous tool in any ways. There is a screw to adjust the length of the support spring which varies the 'arm weight'. The handbook mentions the adjuster but I can find nowhere to tell me what weight I should be using. It's not so much the time taken for cutting but the length of life of blades that concerns me.

I know that hand sawing with a hacksaw can make a big difference in cutting rate, depending on hand pressure so there must be some optimum. I imagine I could get a clue if I was bright enough to translate what the "feeds and speeds" information about turning and milling offers but a simple rule of thumb would be nice to have.

Any ideas about sources of that info?

It will vary, depending on material being cut, length of cut, saw blade tooth count and type of blade, I would think.

‘Sucking and seeing’ comes to mind. There must be a reasonable range, or users would need yo be making changes all the time while cutting round stock.

The only hint they seem to give is in the ‘Troubleshooting’ section:

Bad cuts (not cutting square)
1. Feed pressure too great
1. Reduce pressure by increasing spring tension of the saw

… apart from that, it’s just

“• Let the weight of the saw provide the cutting force.”

MichaelG.

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Ref; __

https://www.clarkeservice.co.uk/manuals/woodworker/CBS45MD_Bandsaw_ISS_5.pdf

Edited By Michael Gilligan on 28/04/2022 06:47:33

I find if you apply too much force, wind the tension spring fully off, there is a tendency for the blade to snatch on break through causing the blade to be thrown off the wheels. This is more pronounced on wider flats rather than rounds where the cut lessens as you cut through. So a bit of trial and error with setting, but once set hardly needs touching again.

Although there will be an optimum it depends on more than the cutting pressure: material, number of teeth per inch. and saw-speed come to mind.

I don't think the arm weight is critical: sufficient to cut rather than rub is 'good enough', and not so much pressure that teeth are forced deeper than their cutting depth. Also bad to apply so much force that the blade bends, breaks teeth, slips on the drive wheels, or stalls the motor!

In theory, I should change the blade and switch pulleys to increase or decrease blade speed to suit the material: Aluminum is much faster than Steel. In practice, I don't bother! Instead the bandsaw is set for mild-steel and allowed to get on with it. I don't fine tune the saw because I cut a variety of metals and diameters rather than a single size and material, and the benefit to me is taking the fag out of handsawing, not maximising production or minimising blade wear.

The bandsaw is the unsung hero of my workshop. Wartiest tool I own and I just take it for granted, yet it saves me lots of time and energy.

NDIYs suggestion of experimenting is probably the best way of adjusting the saw if you must. Rule of thumb is 1HP will remove 1 cubic inch of mild steel per minute. So, with a wattmeter on the input and a large lump of mild-steel in the saw, measure the volume of metal cut per minute. Arm weight is adjusted until the wattmeter shows the motor is near maximum rating, and then blade speed is adjusted for maximum metal removal. Comparing metal removed with the cubic inch per minute rule shows if the saw is cutting efficiently or not.  Note a sharp saw behaves differently to a blunt one!

Unfortunately, this optimises cutting efficiency by brutalising blade and machine. Cooling and lubricating the sawblade is mandatory when cut rate is maximised by industry, but not really worth doing on a small Clarke bandsaw. Instead, the life of the blade is extended by slowing down and decreasing arm pressure. This reduces the cutting load on the teeth and allows them plenty of time to cool down between cuts. It's also much kinder to the motor, which is unlikely to be continuously rated on less expensive saws. The saw's default setting should be fairly close: arm pressure somewhere in mid-range, not too light or too hard.

Industry put massive effort into optimising cutting efficiency, but my feeling is it's rarely necessary in a home workshop. Tools last reasonably well provided the operator avoids rubbing, mincing swarf, and gorilla cutting.

Dave

Edited By SillyOldDuffer on 28/04/2022 09:49:21

Thanks for all the responses. Fortunately, the (second hand) saw seems to behave very well and gives a 'good' square cut. So far, two of the blades I have used have left a good finish but the newest blade seems to leave a more grooved finish. On occasions, the blade is thrown but increasing the tension always seems to sort that out. Some past threads on ME suggests that I may have to get into more than just tension eventually. Fun fun fun. ...

I have to say, I'm a bit disappointed that 'suck it and see' is as good as you guys can come up with but the sources I can find on the internet also seem to avoid committing themselves on the matter. I guess the feeds and speeds and angles are, in practice, a lot less rigid for the home operator than the books would suggest. The 'old guard' seem to talk in terms of the right sound and the shape of chips are the best indication for turning and milling and I am certainly 'getting there'.

I think I'll have to use my fishing scales to find the arm weights that I'm actually using but that seems to be a stage further than ME seems to use.

On the subject of lubrication, cutting aliuminium seems to be faster without lube because the swarf seems to clear better without clogging. Maybe the life of the saw is comprominsed if I stop lubing.

Hi Andrew, yes it is a little guess work, but if you cut a flat bar say 50 x 6mm, with it clamped in the vice by the 6mm dimension, you will need to have less pressure on the blade than you would if you held it in the vice by the 50mm dimension, not having enough pressure on the blade this way will give the effect of the teeth rubbing rather than cutting. You have be aware that these machines are a bit of a compromise, compared to an industrial machine, where the pressure can be controlled by hydraulics even during the cutting process, so in the case of large diameter round bar on an industrial machine, you can start of with a fairly light weight cut and then increase it as it gets towards the middle section and then back the weight off once it has past the middle section, thus prolonging blade life, but in my experience, nobody really does that in a work environment, as they just what to cut things off as quickly as they can and don't worry about how many times the blade has to be changed.

Regards Nick.

Edited By Nicholas Farr on 28/04/2022 13:08:44

Perhaps the number of teeth per inch on the blade you are using is too high when cutting aluminium rod/bar to allow the swarf to clear.
I use 8/10 tpi on a horizontal band saw but that is still on the high side for thick sections.

Emgee

typo edited

Edited By Emgee on 28/04/2022 13:34:27

Edited By Emgee on 28/04/2022 13:36:01

I have to say, the 'mechanics' of this forum are really well below average. When I've mentioned this before, people have leapt to its defence but in 2022, I can't believe this is the only forum they use. Is no one aware of just how convenient and productive the 'recent' innovations are. I find it so inconvenient, even just to quote from other posts; other fora have had a proper facility for at least ten years and, for some amazing reason, the shorthand facility to add likes and other comments to posts is deprecated . Also, why is there such hassle involed when I want to insert an image? I can't imagine that the ME members who want these things to stay the same would have refused to use advanced materials or tools in their machine shop as a matter of principle. Where's the difference.

The situation puts me in mind of a conversation I overheard, at a computer fair, between a man (well over forty) who was busy explaining to his wife that a computer mouse was a waste of time and that the cursor keys could do everything you could ever need to do.

I don't think anyone has gone to the trouble of working out the optimum feeds and speeds of model engineering size machine tools. I think I have only seen one 'f&s' list that also gave the hp required to use them - it didn't go below 2hp.

When I go to Rapid Metals and buy something that needs cutting it just get slung in the vice on a bandsaw as big as a car and cut, they don't mess with the speed but they do wipe the coolant off.

This reads like the old joke: "Everyone's out of step but our Joe".

I use a number of equally technical (if not more so) fora and the short hand is used to great effect yet not excessively so, There is nothing to say that the 'new fangled' ideas will be bad to use. What did you have in mind that makes these extras "an abomination"? No one is forced to use them.

Did you ever consider that some potentially valuable contributions don't reach this forum just because of its outdated procedures. Is it something to do with not wanting 'that sort of contributor'?

And "text based"? Mechanical systems are very much based on diagrams and other images (and formulae). This forum actually suppresses these things. Is that really a good thing? Is additional media a serious risk to the spirit and usefulness of this forum? Are your comments based on your experience of more up to data technical fora? Or do you just not like change? Perhaps we should correspond by postcard?

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I do not wish to speak for Frances, but will respond to that question for myself:

The use of ‘Auto Smilies” on this forum is utterly crass, and yes we are forced to ‘use them’

[ or at least to use tedious work-arounds to avoid them ]

… They could be switched-off in software, but our hosts refuse to do so.

MichaelG.

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… and I’m a bit disappointed in your reaction

From the Supplier’s own guidance [which I quoted] … there is clearly a prescribed maximum pressure, and the only reason for reducing from that is if you are getting ‘bad cuts’

Doesn’t look like a particularly arduous bit of sucking to me.

MichaelG.

What are “auto smilies”? There is nothing automatic in a proper forum. It’s important to make choices based on valid information.

I wouldn’t want TikTok; just some worthwhile improvements.

sorry for my reaction but it was no trouble for me to measure the forces on the handle which is between 10 and 20N so I would have expected someone to have been there too and work out their blade loading. (Much easier than the equivalent with other cutting machines).
I’ve been trying too hard to follow the professionals, I think. Not appropriate for my <500W motors or my rattley ways.

i couldn’t find any figures on a prescribed maximum pressure (load?) on the Clarke manual. Mine’s the 41/2 inch version. I will avoid numbers here and look at results more.

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Probably a misnomer on my part, but they are the automatic substitution of a smiley for a perfectly innocent sequence of characters.

Try typing 1” in parentheses, without spaces

MichaelG.

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(1&rdquo

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The prescribed [albeit not enumerated] maximum pressure is that provided by the weight of the saw

To repeat the quotation:

“• Let the weight of the saw provide the cutting force.”

MichaelG.

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P.S. __ It is my belief that I referenced the correct manual for your saw

… which is quite widely referred-to as having a capacity of 4 1/2” x 6”

… I may, of course, be mistaken

.

Ref. 

Edited By Michael Gilligan on 28/04/2022 22:54:23

That is no help whatsoever. The "weight of the arm" is not the same as the force on the blade because of that massive / adjustable spring that partly holds it up. I read all that already. Can you tell me how I could get the information I wanted? I mentioned that I measured 10 to 20N on the handle but the range is greater than that in both directions. If I remove the spring, then I will get "the whole weight" acting on the blade. I don't think I'm being particularly thick about this when I say that the information is just not there.

But I now realise that it's only by looking at the resulting cut or time taken that I could tell if the spring should be wound in or out if indeed it makes much difference.

But hats off to Clarke on their fantastically good (cheap) workhorse. It cuts much straighter and truer than I could ever do by hand. The only snag is that at least two values of tip are needed and changing the blade is a bit like crocodile wrestling - so I will stay with a fine one and be prepared to wait ages to cut a thick aluminium bar.

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Evidently, I cannot

I have already tried to explain that the maximum is the ‘natural’ weight, and the spring can only serve to reduce the ‘effective weight’ AND that the effective weight is to be reduced if the cutting is ‘not square’

… and I really can’t be bothered trying any further.

MichaelG.