P-Power hacksaw

[John RuddParticipant @johnrudd16576]

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

[Chris BaetensParticipant @chrisbaetens16442]

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

[not done it yetParticipant @notdoneityet]

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.

[Chris BaetensParticipant @chrisbaetens16442]

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.

[Chris BaetensParticipant @chrisbaetens16442]

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

[HopperParticipant @hopper]

Posted by Chris Baetens on 16/04/2017 19:42:58:

Eric,

Busy designing this hacksaw this very moment. It will be capable sawing rather thick diameters. I was thinking about 100mm(4" max. It"ll take some time to work through 100mm steel or brass with this hacksaw but I'm not in a hurry at all….

 

Chris

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

[Chris BaetensParticipant @chrisbaetens16442]

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…

[Ian PParticipant @ianp]

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

[Ian S CParticipant @iansc]

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

[Chris BaetensParticipant @chrisbaetens16442]

Posted by Ian Phillips on 18/04/2017 14:07:17:

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

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.

[not done it yetParticipant @notdoneityet]

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.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Chris Baetens on 18/04/2017 16:32:46:

Posted by Ian Phillips on 18/04/2017 14:07:17:

…

….

I know, I'm not in the right forum to say things like this, but please let me explain.

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

[Neil WyattModerator @neilwyatt]

Posted by Chris Baetens on 18/04/2017 16:32:46:

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).

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

[Chris BaetensParticipant @chrisbaetens16442]

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…

[Ian S CParticipant @iansc]

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

[Chris BaetensParticipant @chrisbaetens16442]

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

[HopperParticipant @hopper]

Between the novel drive (wiper motor) and the novel material (printed) this project sounds like it would make a great article for the MEW magazine. It sort of combines old-school ideas like the reciprocating hacksaw and cheap motor drive with modern technology of the 3D printer. IT would make interesting reading and pics in an article for sure. It is certainly something that has never been covered before (AFAIK).

Edited By Hopper on 19/04/2017 11:36:07

[HopperParticipant @hopper]

Back to the original question of the wiper motor running too hot, it might just be a cheap aftermarket Chinese part that simply is not very good. It happens all the time. Maybe better to get an Original Equipment Manufacturer part, even a used one can be better than the poor quaility Chinese reproductions. I see this type of thing all the time with motorcycle parts.

[Chris BaetensParticipant @chrisbaetens16442]

I bought this motor in UK, so I thought that would be an genuine part…?

[Chris BaetensParticipant @chrisbaetens16442]

Posted by Hopper on 19/04/2017 11:35:19:

It is certainly something that has never been covered before (AFAIK).

Hopper,

After that last remark I immediately did a search on YouTube, and guess what...It has been done before…!
Shame on me……

Chris

[SillyOldDufferModerator @sillyoldduffer]

Posted by Chris Baetens on 19/04/2017 11:59:22:

I bought this motor in UK, so I thought that would be an genuine part…?

Hopper is probably right that it's an after-market motor. The ebay small-print says: "Part Manufacturer: Unbranded".

I can't say if being unbranded is the problem or not. I don't know how hot is normal for a wiper motor and I can't easily get at the one in my Corsa.

Dave

[Chris BaetensParticipant @chrisbaetens16442]

Hey guys,

Did some additional testing. Somewhere in one of the posts higher up I read that the casing itself could be the "-" (ground).
So I connected the powerunit's negative lead to the motor's casing and connected one of the (2) wires coming from the motor to the "+" and it worked to. The yellow wire gave me a higher speed and the white one a lower speed. 75 and 40 rpm.
But.. It also got hot, just the same as before when I connected the two leads white/yellow directly to the powerunit. This resulted in a speed of (about) 100rpm.

[Ian PParticipant @ianp]

Chris

Since you dismantled part of the motor to look at the gears, you may as well look inside the motor and see what's is in there. (and hopefully report back)

The wormwheel in your photograph seemed to show the slipring section that I would expect as part of the parking mechanism but I dont see any wiring to the brush contacts.

The two speed technique I have seen in other automotive motors is with a third brush on the commutator. The two normal brushes at 180 degrees to each other are used for the normal/slow speed. One of those brushes is used with a third which might be say, 150 degrees to it. The supply current is then much higher because there are less commutator segments and less copper in the circuit. The motor is a lot less efficient but its a cheap way of getting the results for the manufacturer.

Nowadays I would have thought that motor speed might be controlled electronically but maybe not in entry level cars.

The printed saw you linked top looked quite good (although a bit of it looked to be wobbling) so I think yours has a lot going for it.

Ian P

 

 

Edited By Ian Phillips on 19/04/2017 18:27:11

[HopperParticipant @hopper]

Posted by Chris Baetens on 19/04/2017 11:59:22:

I bought this motor in UK, so I thought that would be an genuine part…?

If you read the fine print at the bottom of your linked eBay posting, it says "Brand New Aftermarket Part". That could very well be your problem right there. They really do make some rubbish over there. It works good enough to move the wipers and maybe last the 12 month warranty period, or maybe not in which case they give you another unit that costs them about $5 to buy from China. It's a racket. The heat would be from where the aftermarket motor does not have the same amount of copper windings as the original (expensive) and/or smaller, cheaper magnets, so the motor is underbuilt, underpowered and working harder. Wheareas the original OEM part might last 10 or 20 years, the aftermarket part will last one or two years.

Edited By Hopper on 19/04/2017 23:52:40

[HopperParticipant @hopper]

Posted by Chris Baetens on 19/04/2017 12:54:50:

Posted by Hopper on 19/04/2017 11:35:19:

It is certainly something that has never been covered before (AFAIK).

Hopper,

After that last remark I immediately did a search on YouTube, and guess what...It has been done before…!
Shame on me……

Chris

I mean it has not been covered in MEW magazine before and just seems like exactly the type of article that would suit. INteresting video though.

Another thought, you might try to get a heavier duty wiper motor of a larger car like a Toyota LandCruiser four-whee-drive or large American pickup truck etc that would have more power to start with, as it is designed for larger wipers. LandCruiser parts are very solid indeed. More so than little Vauxhall cars, although we don't get that brand here in in Oz these days so I am making assumptions there.

[Author]

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