Dumb Idea Of The Week

"Slow Cut" saws seem to be kind of expensive compared to other chop saws for cutting metal. I was wondering.... why not take something like a SuperPID,
and set it up so you can plug different things into it as needed. Then any tool you have a with a universal brush motor could be variable speed. You could just plug it your regular old chop saw and use cold cut blades in it instead of abrasive blades.
I know the SuperPID brings the price of the chopsaw (if you get a decent one) back up close to that of a regular slow cut saw, but you do not have to dedicate your SuperPID to that one tool.
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Bob La Londe wrote:

I suspect that would result in an unsatisfactory tool. Now if you had a way of putting a gearbox between the motor and blade for cheap, that'd be really cool!
--Winston
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I'm not talking about a crummy little router speed control with a fader or a simple resistance circuit.
Pulley reduction would actually be easier, but perhaps unsafe due to the still high speed and torque. You would basically be building the machine from scratch with that approach.
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Bob La Londe wrote:
(...)

I don't think pulley reduction can communicate the necessary torque within a reasonably-sized tool, anyway. A gearbox is the way to go, here.
This is why I believe:
From a quick search, cold saws run from ca. 22 RPM to ca. 150 RPM. Let's use 90 RPM for S&G.
I see chop saws running at ca. 1300 RPM to ca. 4400 RPM. Let's use 3000 RPM for S&G.
For a given horsepower, the cold saw motor armature and the chop saw motor armature run at the same RPM, it is just that the cold saw arbor has to run at a speed that is 1/33.3 of the speed of the chop saw arbor.
If (on the other hand) you just reduce the average voltage going to the chop saw motor by 33.3 times, what is going to happen to the horsepower at the arbor?
Let's use a 120 V 5 A universal motor and see.
V    I    Eff    HP 120    5    0.82    0.659517 3.6    0.15    0.82    0.000594
Suddenly our chop saw is only good for < 0.1% of the horsepower of a cold saw! You could make much faster progress with a hack saw and still have time to file and sand the ends to perfection. :)
--Winston
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In that case a 4x6 bandsaw already contains the motor, reduction gear and table with vise. Add a saw blade arbor and change the drive direction with bevel gears.
jsw
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Jim Wilkins wrote:

That sounds like work.
I wonder if it would be easier to make a pivoting 'chop saw' frame to mount a metal cutting circular saw?
--Winston
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The thing about using a PID for this is that you pair it with (or often it comes with) an optical tach and it increases power when the RPM starts to drop. Seems like the only real issue would be motor cooling since most universal brush motors spin their own internal fan for cooling. A simple spot of white paint works with many optical tachs as a reference point. I have a hand held that use reflector tape, and half the time I just grab my white paint marker because its handy.
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Bob La Londe wrote:

Even with forced cooling, the motor would probably burn out long before one could do much useful work. That 33.3:1 mechanical 'impedance mismatch' would bite ya. (IMHO).
--Winston
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I hadn't heard of the SuperPID until this subject was posted. The module appears to be kinda-like a hybrid DC-type controller, except with a LCD display added, but using a single triac and microprocessor for controlling AC/DC universal motors.
Controllers for DC motors (wound field or PM types) have the same capabilities as the S-PID, but without the LCD display, and generally use an SCR (or more than 1).. they're capable of maintaining a fairly precise/regulated operating speed while the motor is under load.. and can be controlled by a variable low voltage from a computer port, or just a speed pot (KB, Minarik and other DC motor controllers, for example).
Using some types of motors at speeds which are considerably slower than normal operating speeds will likely present a decrease in a motor's normal power output capability.
The differences I see between expensive cold saws and a basic chop saw, are that a well-built cold saw's effectiveness is based on machine rigidity and workpiece feed features, whereas a chop saw just provides a work stop or vise on a base with a circular saw attached.. not an especially rigid setup, just a convenient means of combining a workholding feature with a circular saw (more practical than a hand held circular saw with the workpiece held with the other hand/resting on a sawhorse, for example). A typical metal cutting chop saw (with a metal blade) is likely to be more efficient when running at (or near) it's designed operating speed.. although depending on the application (metal type or workpiece - tubing vs solid barstock) it may not be the optimal tool. Options typically include different blades for different materials.
Chop saws intended for use with abrasive disks are likely to be more effective at metal cutting when used with abrasive disks.. with options of different disk materials/grades for different materials.. although they do present a flying abrasive debris area which is detrimental to other machines.
FWIW.. A cheap router speed control provides variable speed for AC/DC universal motors, but not a tightly regulated speed when the motor is under load.. essentially a heavy duty triac-type lamp dimmer.. handy for providing variable speed (for universal motors) or variable temperature from resistive heaters.. but not regulated speed or temp. An example is the HF router speed product (spec'd at 15A max) has an AC receptacle for power tool AC cord plugs, which means it can be used for several different power tools, providing variable speeds levels, but without the speed regulation, control source capability or the LCD display of the S-PID.
--
WB
.........


"Bob La Londe" < snipped-for-privacy@none.com> wrote in message
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Wild_Bill wrote:

Nice writeup, WB.
For me the proper answer was to just buy a dry saw. I got the Makita LC-1230 a few years ago. It works a treat.
--Winston
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Yep, many applications are just completed more effectively/efficiently by a particular tool/machine.
The Makita model looks like cutting a wide variety of stock would be almost effortless.
Bang-for-buck value, I believe the 4x6 vert/horz bandsaw is a great tool.. but there are limitations which require other tools. I got my 4x6 almost 10 years ago for $150 when Homier came to town. I did quite a few modifications to it, but after all, they were metalworking.. so sayyourname-sayyourname (win-win).
I don't like cheap offshore induction motors, so I put a used Dayton 1/3 HP motor on it which was a $5 flea market purchase that I disassembled, cleaned, inspected etc and it hasn't caused me any problems since.
I have a Panasonic cordless metal cutting circular saw (garage sale dirt cheap bargain) which is spec'd at 5/8" max thickness in steel, although I don't have any ship building or armored vehicle projects lined up yet, so no actual performance review/opinion from cutting a lot of heavy steel plate. These cordless metal saws' typical uses are construction/fabrication work involving rebar, conduit, U-strut, light channel/angle/stud etc sawing, which is much faster than using a reciprocating saw.
As suggested in the earlier reply, handheld saws' performance will vary due to numerous variables such as the operator's habits and something to hold the workpiece securely (which may be the same thing) when many users just put the material on an upside-down 5G bucket and hold it with one foot.. not a practical or particularly safe or effective practice when a really sharp, high speed blade is in operation while the user is balancing on the other leg. With the material firmly secured to a workmate-type table, the user should definitely benefit from much better results in improved performance, accuracy etc.
Neither of the above tools would significantly benefit from a variable speed motor controller for Bob's original question, but are just examples of different saw types which perform much better than others for various tasks.
--
WB
.........


"Winston" < snipped-for-privacy@BigBrother.net> wrote in message
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Wild_Bill wrote:

It is.
I've cut thick - wall 2" x 4" U channel, 1" bar, 1-1/2" thin wall equal angle and some 2" square tube (all mild steel), aluminum in various cross sections and even some fir 2 x 4 s with it.
It's a good tool.

I've been through two of those. They are terrific if you get a good one. I wore mine to the extent that I couldn't tighten the blade sufficiently to get a straight cut.

Heh!
Yup. I replaced the motor on one of my saws. That motor is now powering a drill press in a friend's shop after I scrapped the saw.

Sometimes I think a manual hack saw is faster than a Sawzall!

I concur, Dr.
Still, it would be nifty to have a variable speed cold - or dry saw. I could slow it down and use the inexpensive high-tooth-count blades.
--Winston
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I was wondering about how versatile the 12" Makita blade is when I looked at the features and specs, and was pondering the fixed speed aspect and how that might effect various styles of blades.
I see a lot of carbide-tipped blades when looking around, and some of 'em are very inexpensive, at least much less than I would've expected. OTOH, there are also some very expensive circular saw blades.
It's a kinda funny contrast here, as there is a Fastenal distributor located just about 50 yards from a Big Lots store and the comparison between quality and pricing is a bit extreme.
In home or small production shops, a particular saw blade type used just for one type of metal (brass for example) may differ from the blade type used just for steel, when it comes to optimal blade life.
Do you use any cutting lubricant at all with your Makita saw?
There seem to be many choices of different tip grades and different tip grinding angles/styles, some of which probably are well suited for completely dry cutting.. although I tend to lean towards believing that a little cutting lubricant (even wax stick) should (maybe greatly) improve the cutting action and extend the life of the blade.. whether the blade might be a hand hacksaw or powered one.
The fast, accurate clean cut of the Makita you have is by far more practical and efficient than one can achieve with a typical Chinese 4x6 bandsaw, for sure. After some shimming and other improvements, I was able to get my 4x6 to cut straight, to the point of making a cut of about 5" in steel plate clamped in the vise vertically.. where the end of the cut was only off by the width of a sharp scribe line. A widely used comment wrt the 4x6 is.. you can be doing something else while the saw is cutting, however I can see that a chop saw like your Makita would definitely make quick work of a lot of accurate, clean cuts in the same amount of time.
--
WB
.........


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Wild_Bill wrote:

The 60 - tooth carbide blade that comes with the LC-1230 is excellent for ferrous metal and lasts a long time. It is also more than $100 a pop. It will cut everything except hardened steel (like bed frame angle for example). I have not tried it on stainless.
So mild steel, plastic, aluminum, wood are no challenge. The 1300 RPM speed means that it takes longer to get through lighter materials than would a fast 'wood cutting' saw, but the extra half-second or so per cut has not slowed me down significantly.

A little secret: I've been using commodity 12" carbide blades in the last few years. They don't last quite as long as the factory-specified blade, but they do a very good job over a reasonable period of time for only ~$35 a pop from my local Home Depot.
It's a pity HF stopped selling their 60 tooth version because they are letting other stores have that profit.
http://www.tools-plus.com/freud-d1244x.html
These blades don't 'wear out' in the traditional sense. They become unusable when too many teeth shatter.

It's almost comical!

I agree. I'm a pragmatist though, the blades I use are a very good compromise for the materials I cut.

I don't. As more experienced folks will tell you, carbide can be run with higher speeds and feeds than HSS and is normally used dry because it can fracture with thermal shock if coolant is interrupted. The chips fly off quite hot but the workpiece remains amazingly cool.

You are certainly right, as a generality. I find the wax stick very useful with my band saw or hack saw for example. The dry saw is used without lubricant though.

That is what I've found. I expect that there are HSMs that have had better luck with their 4 x 6's than I have had or have installed a brace that prevents the problems I've seen WRT blade tensioning.
It is pretty disappointing to watch the band saw cut wander far off the scribed line even with a new blade!

Good on ya. You should publish because there are any number of us out here that need to know how you did it.

Yup. The Makita is much quicker and cuts straight.
If one could tune up their 4 x 6 as you have, so that it cuts straight every time, the band saw would have some advantages over the Makita.
1) The band saw is much quieter 2) The band saw is much less messy (hot swarf!) 3) The band saw generally won't tweak the end of thin angle stock during miter cuts. Sometimes the Makita does. (I just bend it back. No biggie.) 4) The Makita sometimes ejects smaller 'scrap' pieces with impressive speed. I make sure no one will be in the line of fire when I cut.
Having said that, I'm not going back to a band saw for steel any time soon.
--Winston<-- So many projects! So little shop!
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wrote:

Interesting. Is that when they're used on metal, or wood, too?
But you like them, overall? I have one in my Amazon wish list for the time my original miter saw blade dies. $31.89 with free shipping. I have a little 7-1/4" Freud in my circ saw and it has been troublefree for a long while now.
I've used a brand new ($2.50) 24T HF blade in the circ saw for cutting metal roofing to length if I don't use the snips. Double eye and ear protection is in order. Wow!

Extreme opposites on both counts, huh?
-- It takes as much energy to wish as to plan. --Eleanor Roosevelt
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Larry Jaques wrote:

(...)
Mild steel. I've not seen any chipping with wood.

Yes! I use them very far 'off label' and they still work great!

That lines up with my experience.

Heck of a sound board ya got there.
(...)

Yup. Sometimes 'really cheap' is way better than 'really good'. I call this the 'Halloween Decoration' theory. :)
--Winston
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wrote:

Bueno.
It was my first thin kerf blade and it works pretty well, despite it feeling purtdamn tinny.

I did it for the neighbitch. She's the one who brought in 7 horses (on a sub-3 acre plot) and built up the little barn to triple its size. The barn used to house hay. Now it fills up with horseshit daily. Did I mention it's directly upwind?
She's why I'm laid up with poison oak all over me right now, too. She refuses to cut back her wisteria or the tree which was about to take out one of my lilacs. So, while I was cutting her tree branches that were hanging over my yard, I whacked a few wisteria lianas. Well, that's what I thought they were until the next day. Now I'm PINK all over.

Hmm, I wonder if the other neighbors would notice that it was a real body in a Texas necktie hanging from a certain tree next Halloween...
-- It takes as much energy to wish as to plan. --Eleanor Roosevelt
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Larry Jaques wrote:

(...)
OMG.
Arrgh. My bottle of calamine lotion has saved me Much Suffering.
(...)

I know you meant to say: "I Keed I Keed!"
--Winston
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wrote:

She told me that I could take my trees down on her field there, but I came home from work one day and there was earth moving equipment working right there. (Luckily, they didn't collapse my leach lines.) When I confronted her, she said "Oh, I forgot, and I had to act immediately because these guys had some time to do it."

I wish it worked better. Caladryl. I'm about ready to try hair spray. Y'know, lacquer that shit up so it doesn't travel. It's the pink diaper that gets to me the most.

That's enough of that, Peanut. <g> Besides, I never said -I'd- do anything, or what neighbors, or what neighborhood. Wishes and action are two very different things.
-- Worry is a misuse of imagination. -- Dan Zadra
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Larry Jaques wrote:

(...)
Yeouch.
I hope you feel better soon.

Triumph the Insult Comic Dog. Rather!
--Winston
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