P-Power hacksaw

Ian,

The two leads go directly in the motor. If they are connected directly to the brushes I cannot say. Do not know if it is a two speed motor.

This type of hacksaw will eventually cut through very thick bars. I do it with a similar power-hacksaw(also own design) I've built a while ago, also driven by a windscreen wiper motor of the same size. I just want to replace my existing power-hacksaw with a much smaller one. Goal is to make it only (about)300mm-1'- long. The one I'm using now is way to large and most of all to heavy.

And yes it'll take some time to cut through thick bars, but I don't care. To give you an idea, to cut a 50mm-2"-brass bar with my existing hacksaw takes me about 35 minutes. During the process I apply only a little bit of pressure on the blade.

Edited By Chris Baetens on 17/04/2017 09:53:07

An old 12 volt Lucas wiper motor would be ideal for a small power hacksaw, it will take anything up to 24 volts, I run one on the table fed for my mill on 18 Volts.

I also run a mini power hacksaw on a hot air engine, it has a Junior Hacksaw blade. I know mine is not plastic, but I'm sure something mostly plastic could be made.

Ian S C

I played with that thought, to make a hacksaw driven by a Stirling engine, but in the end I didn't know whether it would work or not.
But now that you mentioned it, do you have drawings to build that Stirling engine powered junior hacksaw. Don't know why but the moment I read it, I instantly started drooling...

Obvious solution to overheating motor is 'Water Cooling'

Never like to mix electrickery and water, but it's being done inside confuters to cool the processors now, so why not around a wiper motor?

Regards

Richard.

Have you considered that the motor may be a two speed job?

The negative connected to the body of the motor and the positive connected to one of the two wires for the two speeds?

Ordinarily, the brushes would  be opposite each other with half of the armature connected across the supply, with a third brush contacting a reduced number of coils, would give a higher speed but an increase in current.....

Edited By John Rudd on 17/04/2017 18:48:39

Meanwhile, did some tests and had the motor (free)run a few times for a couple of hours. I placed a 80mm fan, very close, to the side of the motor and it got less hot. This will be the solution I think. Still, the motor gets about 40°C, I'm only guessing. I can hold it in my hand without any discomfort.
Afterword I took it apart and discovered that the wormwheel's axis is running on a plain metal bushing, not even bronze..! For this kind of torque, and especially when this motor is expected to run for a 'lifetime' I would expected ball bearings around that shaft. Nevertheless, I will continue integrating this motor in my hacksaw.
Main challenge to build this saw will be mounting a crank to this motor. Problem is the visible part of the wormwheel's axis is nothing more piece of threaded rod M8 only 10mm(3/8) long and also a ribbed conical piece barely 7mm(9/32) long. But that's part of the fun...

Edited By Chris Baetens on 18/04/2017 10:15:29

Edited By Chris Baetens on 18/04/2017 10:15:55

Two wires will almost certainly be single speed. One for run and one for parking.

A 24V lorry or coach wiper motor would be far better, IMO. Automotive drives are not generally designed for efficiency - just minimum size and mass. Think of the efficiency (or lack of) of the average automotive alternator generator.

To cut 100mm will need a blade of at least twice that? Othewise the gullets will not clear? Getting tight for designing it at only a foot in length, I think.

I need some explaining to do : The sawblade itself is a standard 300mm-12" long blade. During action the 'sawbladeholder' will move a few inches past that 12" long ground board in both directions.

This is how this wiper motor looks like when cannibalized.
The motor itself runs at about(estimate) 2000rpm

Cutting a 100mm diameter steel with a wiper motor is a big ask. Commercially made power hacksaws of that capacity will usually have at least a 1/2 horsepower motor but it seems you have done this before so we can't say it can't be done!

Interesting concept though, to make it out of 3D printed parts. What kind of printing material will you use to take the stresses of tensioning the blade and withstanding the reciprocating motion under alternating loads? What size blade do you plan to use, a hand hacksaw blade or the thicker power hacksaw blade?

Edited By Hopper on 18/04/2017 13:01:44

Eric,

I'll be using the same blades I always use in hand hacksaw. Works just fine with my old power hacksaw. I regularly cut 120mm aluminum bars and also 50mm brass, the cuts are perfect and straight.

I will use PLA to print most of the parts. PLA is very stiff and at the same time very strong. Some parts will not be printed of coarse, like the groundboard,..

Maybe, just maybe I'll print the vise to...

Chris

I wish you all the best (seriously) in the construction of your power saw. I think if it performs as well as you hope quite a few people (including me) on this forum will be very impressed.

Whatever the vise is made from I am visualising your whole machine being held to the bar you are cutting, which in turn is held in the bench vise

Ian P

There are no plans for my little saw, it just sort of happened. The drive from the Stirling Engine (in this case a Ross Yoke ALPHA motor) is about 4:1 reduction, on the saw is another geared reduction of about 2:1, the saw stroke is about 1 3/4", and it will cut a 10 mm steel bar in about 20 minutes, not bad for 5 Watts. When it is run on the 180 Watt motor that powers my Super Adept lathe this time goes down to about 1 minute. With a wiper motor similar times could be obtained. With the SE it is not entirely practical, but it does demonstrate that a little SE is not entirely useless, and it is something other than a generator, or water pump for the motor to run.

Older wiper motors had wire wound fields, I don't know if this is an advantage, but I'v been using my old Lucas for something like 20 years and it seems to be OK running on 17/18 Volts, A 24 volt motor would take 40+ volts, and be more flexible.

Ian S C

I can imagine what you must thing about this project Ian, and maybe about me to. And I think you're not the only one.
May I explain a bit about myself please : I'm not a spring-chicken anymore, I am a mechanical engineer, know my way in 3D-drawing(Autodesk-Inventor), Know my way rather good in 3D-printing. I even designed my own printer, designed and printed lots of things with it. The largest thing I printed so far is a (rather large) telescope.(scroll to bottom of page).
Most importantl, I want to do things (most of the time) a bit different.
A long time ago I started my carrier with 2 drill presses, a lathe, and a large milling machine. Until a few years back a made Stirling engines, had lots of fun making these. And then, 3 years ago I bought a 3D-printer. And that's when it all changed.
Every time again, when I start a new project, I step into my workshop, the first thing I have te decide : How will I proceed with this new project : will I use my mechanical machines or shall I print it, or just maybe I will use both techniques combined...? Very often I'll go with the printers, because there's almost no limit what I can do with it. I mean,comparing the possibilities using lathe/milling to printing, my choise is very quick made. I know, I'm not in the right forum to say things like this, but please let me explain.
When I draw a very complex object in Inventor, there's absolutely no way I can make that object with a lathe/milling. Even with CNC machines, believe me. I can show objects I've printed impossible to make the classical way.
Will this powered hacksaw work, well I do not know. I think it will. While drawing it I will be forced to think ahead and balance what will be printed and what will be made by other means. Goal is of coarse to print as many objects as possible.

This an example what I can do with a 3D-printer. There are 8 holes in this part that are angled. When this XY-carriage is completely assembled, it will contain 14 ball-bearings, that are perfectly aligned. Through this block runs also a square hole to allow electronics to be mounted and the wiring for it. Most of the holes will be reamed.

Printtime for this object : about 5 hours. This part is printed to make me another 3D-printer.

We have had a recent post beefing about cutting aluminium with a hacksaw, let alone steel!

All things are not quite equal, but that 10mm bar, that Ian S C found took 20 minutes to cut through, extrapolated to 100mm diameter would take about 2000 minutes - yep, best part of a day and a half - to sever.

50mm brass to 100mm would extend the cutting time from 35 minutes to near 2 1/2 hours. Change material to steel (even free cutting, not a tough carbon steel) and it will take very much longer. Possible handraulically, given time (and no tennis elbow), but I would most certainly not relish the task, even if using a better saw and blade than the normal hacksaw!

An interesting project.

Many thanks for providing more detail Chris. I'm sure I'm not alone in thinking that what you're doing is interesting and impressive.

Good luck with the hacksaw. 3D printing has huge potential. Please keep us informed, warts and all.

Cheers,

Dave

That's a very nice looking scope Chris!

Foe what it's worth, I can see no reason why 3D printed parts won't work. The more experience I get of them the more I realise how robust they are. You just need to develop a new 'eye' for working with these materials - making a Prusa from a kit has taught me an astonishing amount about how to use printed parts. Looking at Thingiverse has also given me some good ideas as well as some ideas about how NOT to use them!

Neil

Edited By Neil Wyatt on 18/04/2017 20:09:08

Neil,
We not only need to develop a new 'eye' for working with these materials. We also need to have een open mind and except,that this new technique is now in our lives (and our workshop) to stay,.forever...

There are only a couple of areas that might need some thought, the stiffness of the frame with the blade under tension, and the sliding surface of the frame on the arm, the arm would be well served by a stainless (?) rod from a photo copier (maybe two, side by side). I know nothing of 3D printing.

On my saw the vice is about 1/2" wide, and opens to 5/8", fabricated from scrap steel to look like something that would be on a full size saw. The screw thread is 3/16" UNF, it's just a case of using what ever comes to hand.

Ian S C

Ian,

The frame holding the blade should be very stiff and strong indeed. That's why I'll use a steel rod.
The sliding part will be made using ball bearings around that steel rod.

Chris