Thread: 18v cordless circular saws

I actually think that, for a right hander, the motor on these saws is where it should always have been. Mine (Metabo) works fine in my right hand and my eyes are more easily over the blade.

I'm right handed & have got a Milwaukee M18 Cordless saw and have found it quite good to use even on docking some 4x2 hardwood. cheer, crowie

As far as seeing where your line is it is easier to use but if your are holding the piece of timber in your left hand the weight of the saw tends to sit on the off cut piece and can make your cut a bit skew if. The weight of the saw should stay on the side if your intended cut length. How do you find the milwaukee for cutting power and comfort. I have been looking at the new metabo 18v and it looks ok but has 2700 rpm at idle and the milwaukee is 3500. Does this differance make one better than the other?

Originally Posted by Dobre

As far as seeing where your line is it is easier to use but if your are holding the piece of timber in your left hand the weight of the saw tends to sit on the off cut piece and can make your cut a bit skew if. The weight of the saw should stay on the side if your intended cut length. How do you find the milwaukee for cutting power and comfort. I have been looking at the new metabo 18v and it looks ok but has 2700 rpm at idle and the milwaukee is 3500. Does this differance make one better than the other?

G'Day "Dobre",
I haven't had any difficulty with the Milwaukee M18 saw, I've even used it to cut 6" hardwood [four cuts] and it went well, with a shape blade.
Maybe the higher speed helps clear the sawdust as it's spinning through the timber.
Battery life has been good but I've only had the tool 2 years.
As far as seeing the line, I have to use a straight edge to get a straight line as a DIYer and not a carpentry tradesmen.
My builder mates have Panasonic cordless saws.
I'm sorry I can't give you you too much other technical knowhow except to say that I've been very happy with the purchase and enjoy trying to make things especially wooden toys & aids for my wife to give to clients [healthcare].
Cheers, crowie

''I haven't had any difficulty with the Milwaukee M18 saw, I've even used it to cut 6" hardwood [four cuts] and it went well, with a shape blade. '' How did you manage to do that?

Originally Posted by Dobre

''I haven't had any difficulty with the Milwaukee M18 saw, I've even used it to cut 6" hardwood [four cuts] and it went well, with a shape blade. '' How did you manage to do that?

G'Day "Dobre".
Just put a square line around the old gate post, managed to line it up reasonably and straight through; had to cut the little square left in the centre with my old hand saw.
I was using it as a post on an outdoor setting table and had to cut 2 of them.
Hit it with the belt sander after I cut it to length and a coat of polyurethane; though the table being all old hardwood is very heavy.
Cheers, Crowie

Hilti are the only other brand I know that make right handed saws in 24volt and 36 volt.

Hi all,

The circular saw blade was invented by the very resourceful lady Sarah Babbett, using the lid of a tin (with teeth cut in its circumference) in her spinning wheel. The story goes that she was somehow able to cut a piece of wooden shingle with it. Such a cutting wheel was again experimented with in 1921, when a certain Edmund Michel sought a way to make life easier for sugar cane harvester, who used machetes in their back breaking work shifts. There was not much compact technology around for him to choose, so he took some suitable components and combined them. A 100 Watts Hamilton Beach milkshake motor was to be the power source and a worm wheel drive array was to spin a small saw blade. The components were built onto a wooden rod (like that of a rake or a shovel), with a switch somewhere on the upper part. The contraption was fed through an extension cord by a generator on wheels, which was taken along to the cane field. The progress was not as swift as with machetes, but using these experimental tools proved much easier on the backs of the harvesters.
Sugar cane harvesting was eventually mechanised in another way, but Michel's idea was evolved into a heavier construction, powerful enough for sawing wood. For that the motor needed to be in the 500-1000 Watts range and electric motors in that range were very bulky and heavy in the 20's. Michel's experience with the worm drive system had taught him the advantage of the worm wheel input axle being tranverse to the crown wheel output axle. So the motor's axle could be parallel to the saw line and needn't be parallel to the saw blade's axle, as with conventional gears. With the motor's bulk lying parallel along the saw blade, the machine's weight distribution and balance could therefore be much better. Michel mounted a rear grip behind the motor's housing and a bow grip at the machine's front. The right hand was for pushing, the left hand for steering. Michel found it best for the (right hand) user to have a good view on the blade and its progress along the pencil line, so he chose a left side mounting of the saw blade. Michel founded the Michel Electric Saw Company, changing it to the Skilsaw Company in 1924 after finding a business partner for marketing and bookkeeping. The Skil 77 worm drive saw has had its blade on the left side ever since, and so have the spring-off models from competitors (Milwaukee, Makita, DeWalt and Ridgid). It is simply the most convenient setup for precision results and good control.

How the saw blade eventually became mounted at the machine's right side, was a patent matter. The two brothers Porter and their partner Cable founded manufacturing corporation Porter-Cable in 1906 and hired engineer Arthur Emmons in 1921 to start up an electric tool development team. Emmons designed the first portable belt sander and also wanted a sturdy circular saw in the company's program, since wood building had a huge scale in the US and electric tools for woodworking turned out to be huge sellers. Porter-Cable had to pay stiff patent license rights to Michel/Skil if they should ever want to copy the worm drive saw, so they chose to avoid this patent altogether and to think up something for themselves. Emmons chose the conventional reduction gears with a motor pinion, with input and output axles running parallel. So he was confronted with the balance problem that the worm drive had so elegantly solved for Michel. There was a lot of motor bulk hanging beside the saw blade and for a better point of gravity and handling balance, it proved best to point the motor toward the user and the blade away from him. With a left-bladed array like in the worm drive saw, Emmons design would have a tendency to tilt, with the motor weight pulling the machine down and away from the user.
Emmons made up for this peculiarity by emphasizing the safety aspect. Sawed-off bits fell away from the user and not on his feet. The blade was pointed away from any body part, with lesser chance of injuries. And by covering a larger part of the sawing blade than his competitors would in their machine designs, Emmons made a visible point of his safety concern.

Because the power-to-weight ratio of battery circular saw motors is much better than the ratio of mains fed saw motors, it has again become viable to put the blade in the ideal left side, where view on the progress and the workpiece is best. Modern low voltage DC motors have very strong field magnets, allowing for much smaller field and overall motor enclosure dimension than copper wound stators could ever offer. With input ratings between 300 and 800 Watts, DC magnet motors are 30% or more compact than mains AC brush motors. The argument of the saw being prone to tilting because of too much motor bulk hanging beside the blade, is no longer valid. The battery pack is no balance argument either, since it is clipped onto of the rear grip or is positioned close to the machine's heartline anyway.

As for voltage, there are some pros and cons. There is a maximum of Amps that can be drawn from a battery, depending on its chemical composure. Tens of Amps can be drawn from a lead-acid battery before it is compromised by its own internal electrolytical process; hydrogen bubbles form, there is a lot of heating and plates may slightly buckle. Hundred of Amps (car starter motor engaged with -Heaven forbid- the headlights on) can only be supplied for a few seconds. Anhydride battery types fare better, like the Nickel-camium or Nickel-metalhydride types. But they too can get very hot and decompose themselves when too much current is drawn. At present, lithium-ion types can cope with the biggest current draws before they overheat or may even explode (hydrogen gas building up inside). The capacity of current flow is alternative called "internal esistance". A lead-acid battery has relatively high internal resistance, a Li-ion typ has very low i.r. They are at present the best choice for high Amp applications (electric cars and even vans, power tools, cordless garden tools and guzzling consumer electronics like fast hi-res still-/video cams).

More voltage means more cells and therefore a bulkier and more expensive battery pack. There is also charge capacity, measured in Ah (Amp-hours). This is a product figure, so a 2Ah battery can deliver 2 Amps for 1 hour, 1/2 Amp for 4 hours or 10 amps for 0.2 hours = 12 minutes. And then there is the maximum efficiency curve of the DC motor. The motor types as used in cordless power tools have maximum efficiency at around 80% of no-load rpm (at that point of the curve, efficiency can also be as much as 80% in quality brand motors!). The load can of course be increased, resulting in rpm-drop, and the motor power will indeed be higher because of higher Amp intake, but the amount of generated heat as measured against true output Watts, is much higher. You will therefore get more power out of a heavier loaded tool, but much less useful work out of one battery charge, because a higher amount of that charge will be converted into useless heat. When you take the 80% efficiency rule as your guidance, than the choice for a higher battery voltage is best. The cells are all the same, so Li-ion cells in an 18 Volt pack can cope with the same amount of Amp draw than those in a 36 Volts pack, provided that their Ah-rating is the same. Suppose that at 80% efficiency, the motor draws 20 amps, meaning that its input would be 360 Watts at 18 Volts and its output 80% of 360 = 288 Watts. This would be the same as the output of a mains fed saw of 500 Watts. This can of course be no heavy duty machine for difficult tasks, it is rather meant for light tasks and finishing and only occasional hevay jobs. But at 36 Volts and 20 Amps, the motor will take 720 Watts and will give back 576 Watts, the same as a 1000 Watt mains saw would give back. That starts to sound like a grown-up solution.

36 Volt saws start to resemble grown-up mains fed saws again and their motors are chosen slightly oversized for heat reserve reasons and for a better fan-drawn internal cooling air stream. So that's why the smaller battery saws have left hand blades (better precision for finsihing jobs) and the big ones have a tendency to return to right side blades.

I'm a left handed user myself, so i've gotten used to the odd handling of right bladed saws, and to tolerate the dust that's blowing right in my face (the same with planers, especially working overhead). I recently tried a left-bladed worm drive saw. What a difference. Heavy, but beautiful! There are also left handed conventional circular saws on the market. Porter Cable has one, and Makita offers two sizes (designated with "L" in the type number). I tried one of those and it really works, but i also value the sight on the blade that is my advantage over right-handed users with right-bladed saws. With a saw built for your disposition, it is much easier to push the machine against its parallel guide to let it slide along the pencil line without straying from it. It merely takes two fingers leaning stretched against the side of the pistol grip, to achieve that steering pull towards you. With a saw built contrary to your disposition, you need to push the saw away from you with your thumb, which is a bit awkward and fatiguing.

My own battery saw is an Elu MHA24. Splendid machine, and by keeping the motor's rpm within recommended nominal load limits, the motor and gears and batteries still behave like new after years of use.

greetings

gerhard

Another insightful post from you, gehard!

Would that be the famous New Yankee Woodworker Norm Abram in the last photo?

Great post gerhard, I have to agree the vision of the cutting liine is better from the left sided blade and I guess getting use to the weight of the saw dropping off the cut off peice is something that you will have to get used to. How does the rpm (no load) affect the circular saw as I know that the higher the rpm the cleaner the cut will be especially when cutting particle board or mdf. For example the 18 volt range of AEG (orange series) 4400 rpm, makita 3700 rpm, Dewalt 3700 rpm,milwaukee 3500 rpm, metabo 2700 rpm, all of these are good brands but which one would have the best grunt (torque). The dewalt line has the new nano phosphate type of battery and I dont know what the differance is with the Li Ion. I dont expect miracles from these circular saws but it is difficult to make a decision when there is a large gap between them when you look at the rpm's. I know people say keep the the one brand as it is easier to have one battery that will suit all your cordless range but if you just have hitachi most of the range may be ok but they might have a crap sabre saw for example. Mixing the cordless tools might be a pain but that way you can have the best of each item.

Hi renov8tor,
thank you very much for the compliment! And yes, it's Norm Abram. When looking for a picture of a guy wielding a right hand circular saw, that was the first one i ran into. This is the link where i borrowed it from:

Choosing and Using a Circular Saw | Power Tools | Tools and Products | This Old House - 1

And hi Dobre,

as far as rpm is concerned, a circular saw is much like a bicycle. There is the racing type bike meant for paved roads (Tour de France style) with thin tyres and a high gear ratio, enabling high speeds. And there is the mountain bike for rough terrain with less extreme gear ratios to cope with muddy terrain and slopes. High rpm for a circular saw gives the cleanest cutting results, like with a router, but is less ideal for large saw depths, because of more friction heat and more problems to get rid of all the generated saw dust. For many professional mains fed saws, the motor is laid out for heavy load and high thermal reserves, meaning that it will survive severe rpm loss (and thus cooling airstream loss, since the fan is mounted on the armature). With this philiosophy, you have a "self regulatig saw", as it were. Rpm stays high in thin material, needing a better finish, and the load rpm will drop with large depth and will automatically adjust itself to that circumstance. For the same philisophy, the series type brush motor was once chosen as being ideal for electric drills. Rpm stays high with a small drill bit and drops when using a large diameter, thus selfadjusting the cutting speed.

I always monitor the sawing progress with my ears (sound pitch difference between no-load and load rpm) and with the dosage of the forward speed. High rpm battery circular saws with a very strong motor loose less rpm on tougher jobs, so you will get more forward speed and sawing capacity out of them. More than 4000 rpm for a 18 Volts saw sounds a little rich, it is probably not powerful enough and looses too much speed or needs you to go ahead at a very slow pace. Brands using a lesser speed (below 3000 rpm no-load) often do so to give a smaller motor better torque figures. So, besides the rpm count, you also need to compare the output powers of the motors at best efficiency. Those figures are hard to find, often they are not mentioned or manufacturers use exaggerated numbers that where measured at overload or near stalling. I will help you look for examples. Till then, bye for now.

greetings

gerhard

The AEG that I mentioned and Metabo AEG POWERTOOLS Australia | Products | Saws | BKS18

Product catalogue Metabo "Building Trade" handheld powertools - Building trade - Metabo Australia - Power tools built by professionals for professionals

Hi Dobre,

back again after some study into the AEG BKS18. A closer look reveals that it is value for money, although technical information on the machine is issued very sparingly, to put it politely. There seem to be two generations of BKS 18 models. In blue livery it started off as a left-side blade type with NiCd-batteries. These have 2.0 Ah capacity and with a predicted input of 180-360 Watts one charge will last 6 to 3 minutes worth of sawing. This earlier type has a 165 mm diameter blade spinning at 2500 rpm no-load (approx. 2000 load speed at best efficiency and 1800-1500 at optimal sustainable motor power without too much overheating). The first pic shows this earlier model, in blue. This is the exploded view:


http://www.aeg-pt.com/internet/aegexplo2003.nsf/Files/401524.gif

This model is now on sale to get rid of old stock. AEG's change of colour (blue to orange) is mentioned as one of the argument to flog the old version. Be sure not to mix it up with the newer and more expensive orange model, since a few sales channels mix up the pictures and sell the old version while showing the new one. When you see "2.0 Ah" and "2500 rpm", there is a good chance that they mean the old version.
During the transition, the design has obviously been revised. The blade diameter and the battery voltage have stayed the same, but the motor power and the battery capacity have been increased. 3.0 Ah charge capacity alows for a higher Amp/Watt motor and therefore an increased no-load speed of 4400 rpm. Best efficiency will be around 3500 rpm load speed; best motor power factor at approx 3000 rpm. My guess is that the motor input is around 400-480 Watts. The newer model (orange) is in the second pic. Whereas the old model was obviously put in the category of finishing jobs with optimal sight on the sawing process (left handed blade), the new version seems to have been dedicated to slightly more heavier jobs, as done with mains fed machines. That and the different balance of the heavier side-hung motor have probably been the reasons to move over the saw blade to the right.
This is the exploded view of the newer model:

http://www.aeg-pt.com/internet/aegexplo2003.nsf/Files/411383.gif

My inpression is, that this machine is value for money. There is a metal gearbox and the blade arbour has at least one ball bearing. The opposite bearing may wither be a sleeve or a needle type. I do not know the motor (there is no info on it in the web), but it has its own fan and "can shaped housing" motors of this size often have ball bearings instead of bronze sleeves. The motor pinion is replaceable, which is a professional approach (all top mark heavy duty saws and angle grinders have replaceable pinions). There is no info on brush replacement. Battery circular saws do on average not see the same work hours as drill/drivers do, but the BKS18 has an electric brake (quick reversal of armature poles) ; a system that is known to generate violent sparking and quicker brush wear, especially at the high Amp rates present in battery tools.
The battery packs have built in electronics, offering protection from overheating, overloading and over-drain of current (auto switch-off after pinching or stalling). The machine's hinges on the sole plate are sturdy enough and the plate itself is of cast magnesium alloy, the best solution possible for these saws. In spite of lightweight alloys, the machines weighs more than 3.5 kilograms without battery pack (more then 4 with pack), which i consider a good thing. For a sturdy machine, there is no substitute for honest weight spent on decent materials, like copious motor magnet and armature bulk and a good set of heavy gauge steel gears and arbour.

Apart from all this, i have little to tell you about the BKS18, since i don't own this model myself and haven't worked with it yet. Of the two models, the new one with 4400 rpm speed and Li-Ion 3.0 Ah packs is the one to go for. For myself i own an Elu MHA24, of which i have added the manual:

http://service.dewalt.co.uk/PDMSDocuments/EU/Docs//docpdf/mha24_eur.pdf

As you will see, this thing has NiCd-batteries, because NiMH were way to expensive six years ago and Li-Ion technology was still in the low-Amp stage of cell phones. The batteries are this machine's weak point, especially their loading and unloading regime memory effect. This is not present in Li-Ion batteries, but those react very badly to overloading (every time you leave a cell phone carging overnight, when it's already full for several hours, you permanently loose a few percents of charging capacity, especially when the charger is a "quick" type with slightly increased charging voltage). Chargers for power tools are on average quick types, so the overload protection on Li-Ion batteries makes good sense.
I love the MHA24, but i know its limits. Its balance is good and so are its sawing results. I respect the best-efficiency rule, so its batteries and motor and gears are still in fine shape. But the stated "maximum 480 Watts of motor output power" are definitely fishy. There is no mentioning at what circumstance this measurement was taken. Is it stalling torque or merely the highest figure they could boast when there was still some productive saw blade rotation? Since there is no certainty about claims like these, they can be considered as useless statistics. As numbers they are high and look impressive on paper as such, but there is no real objective value in them.

Since i covered this topic in a post somewhere above and it comes back again now (because it is important), i looked up some real statistics from battery motor manufacturers, to better illustrate what i mean.

As you know, NiCd-batteries were once as expensive as Li-Ion pack are now. So battery power tools were makeshift and flimsy alternatives, starting off with 3.6, 5.4 and 7.2 Volt packs. The best known motor manufacturer at the time was Mabuchi from Japan, known worldwide for toy motors and car applications (electric window drives, heater fans, car vacs, water pumps for the wipers, etc.). They made a range of low voltage motors constisting of a deep drawn can shaped housing with a nylon closing plate, containing the brush array and the hind sleeve bearing. The 80- and 120-types were typical small units for toys (1.5 to 6 Volts) and the range ent up in size through the 180-, 360- and 540-types. The 540 has become the most famous. It was souped up to drive high power car battery fed car vacs and little tyre compressors, after a career in radio controlled battery powered model cars by e.g. Tamiya. The 540 was fitted with ever more powerful magnets and more heat resistant windings. The strong field made a sleeve necessary around the can housing. In this shape, the 540 was to be found in the first Makita and Hitachi battery powered power tools. The Hong Kong firm of Johnson purchased production licence rights and made the 180, 360 and 540 in virtually unchanged versions, to be sold to budget trademark power tool makers. Makita, Hitachi, B&D, Milwaukee, AEG and others have since improved the basic Mabuchi designs with their own developments (buitl-in fans, ball bearings, brushes mounted in screw caps, esterimide treated coils, magnets from rare metals, etc.)

As a service for development engineers, manufacturers offer specs of their products, to make the match of a power source with the desired tool design specs easier. Here you see the true figures that are held back from end users in the brochures. This is such a spec sheet from a Chinese manufacturer. Their 550/555 is yet another spin-off of the venerable 540:

http://www.alibaba.com/product-gs/359439656/RC550_555_dc_micro_motor_for.html

This motor is not quite in the power league of the 400-plus Watt motor of the BKS18, put the characteristics are the same throughout most of the range of permanent magnet low-voltage DC-motors. You see that there altready is a current draw of some 10 Amps at only 10% rpm-loss at load speed. This is also the best-efficiency range. You also see that stalling torque can be up to 10 times as high as at best-efficiency speed, but the current through the windings then exceeds 80 Amps. Such a small motor is of course not built to cope with that and will burn if such a current is kept up for more then 10 seconds. The low internal resistance of modern NiMH and Li-Ion makes them very capable to keep up such a current with a drop of only a few Volts. But having read this, you can understand the temptation for power tool makers to quote the high torque and Amp ratings, even when these secretly are only valid at stalling situations.

Another good piece of reading is this sheet by Johnson, also meant for engineers:

http://www.johnsonmotor.com/Performance-Charts.266.0.html

Note the red and green graphs. For best service life and battery charge return, the red curve is the one to follow. But this needs a delicate touch, forward sawing speed must be a very moderate pace to keep the rpm high. When the going gets tough and the pace must be more forceful, the green curve shows the max power output of the motor. The saw is truly more powerful in this situation, but the higher Amp flow generates a larger percentage of heat, which is to considered as energy loss (heat output instead of torque output).
Also note, that the Wattage of these motors is much feabler than what is suggested by manufacturers. At best efficiency, a 550 type motor has an intake of only 120 Watts (12 Volts x 10 Amps), but the relatively high output of 95 Watts (which is 79% efficiency and especially good for such a tiny motor; try to find a mains fed motor that can match that, even a big one!) makes up for it. With a theoretical 480 Watts input and 75%, the BKS18 could have an output of 360 Watts. That compatible with a 710 Watts mains fed saw.

To top this story off, here's the BKS18's (3.0 Ah version) manual:

http://www.aeg-powertools.eu/sites/www.aeg-powertools.eu/files/upload/pdf/289044-bks18.pdf

That's all i have time for at the moment. I'll get back to you with a Metabo study, but that will be somewhere after Christmas, because i'll be away on travel.

For now, all the best and a very Merry Christmas( also to other readers)!

gerhard