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Anyone made Myfordboy's powered hacksaw?

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IRT08/09/2019 22:35:06
104 forum posts
32 photos

I need to cut metal, am short of workshop space, and am looking for a project... Myfordboy's powered hacksaw looks ideal.

I have found a few references to it on this forum, and a few YouTube videos.

As far as I can see, those who have made it seem pleased with it.

How many people on here have made it?

Are you pleased with the result?

What are the difficulties I will encounter?

(Progress to date: I have purchased the plans and 3D printed a pattern to cast the pulley.)

Joseph Noci 109/09/2019 07:06:31
711 forum posts
917 photos

At the risk of boring this forum with even more of the same of my photo's...

I built my own version of a power hacksaw, so cannot say if the plans you have are good, but it seems there are quite a few builders out there who are happy with it.

My version also uses Hex bar for the gantry and slide - I did beef up the size of the bar and the blade holder/slide has been strengthened so it does not flex to much when applying blade tension. Also made a hydraulic damper, etc...

Not sure how to give a link to my posts on this as I cannot direct the link to my post exactly..but here goes -

**LINK**

If that does not work - a photo or three..

Joe.

ready to cut.jpg

left view.jpg

saw frame and slides.jpg

 

typo's...

Edited By Joseph Noci 1 on 09/09/2019 07:07:14

IRT12/09/2019 19:40:20
104 forum posts
32 photos

It looks good!

Are you please with the accuracy of it?

I am expecting to take far more than 2 weeks with my build.

Clive Foster12/09/2019 21:29:08
2254 forum posts
76 photos

If you want a quick build might be worth looking into replacing the built up from hexagon bar slide system with one of the linear rail and bearing block systems that can be got quite inexpensively these days.

For example a quick google comes up with complete 20 mm round rail sets with two rails, two rails supports and four bearing blocks at around £35 for 500 mm rails via E-Bay. Which should be long enough. Set horizontally with the saw bow hung between the stiffness should be more than adequate. Nominal "rectangular" rails are approaching twice as much but its likely that rather larger a single rail used with two bearing blocks will be stiff enough. Given the choice I'd prefer dry bearing material plain bush versions but such may take a bit of finding at realistic home shop prices. Igus and other brand name types being too expensive.

Back in the day I used both the rectangular and round rail types with every satisfaction on jobs for the firm. Prices then being very much not Home Shop Guy friendly!

The MyfordBoy saw is basically a home shop builder friendly version of the Kennedy hacksaw. So long as you do a good job with the guide rails it will be as accurate as you can reasonably expect. Hafta say I prefer the U section steel base that Joe used to the MyfordBoy style.

Looking a YouTube videos I'm not completely convinced that the geometry of the saw bow drive is as good as it could be. My Manchester Rapidor power hacksaw has the saw bow drive arranged to give a very effective automatic lift on the return (back) stroke. Putting the blade in the wrong way round gives an excellent demonstration of how effective it is as the reversed blade is barely able to cut. Rapidor saw bow is much heavier too. Although the Rapidor is built "opposite hand", rails fixed to the bow and the slide bearings in the pivoting carrier, the fundamental geometry is the same so it ought to be possible to get equally efficient return stroke lift. Which should do wonders for the life of the blade. Especially if you run it a bot slower than the usal YouTube examples which look far too fast.

Clive

Andrew Entwistle12/09/2019 21:59:40
avatar
78 forum posts
152 photos

Hi Ian,

I made one about 6 years ago (you may have seen it on YouTube) and still get satisfaction from just walking past it in the cellar, but mostly from when I use it to move on a project that might stall if I had to cut the stock manually. It has cut a few 4" plus slices of aluminum and plenty of steel square section for quick change toolposts My mistake in building was TIG welding the hacksaw blade frame instead of silver soldering, making it harder to clean up and align, otherwise straightforward. I was eventually able to achieve the 0.25mm thick slices of mild steel that David Abbot demonstrates.

Andrew.

 

Edited By Andrew Entwistle on 12/09/2019 22:01:46

Joseph Noci 113/09/2019 07:12:58
711 forum posts
917 photos
Posted by Ian Thomson 2 on 12/09/2019 19:40:20:

It looks good!

Are you please with the accuracy of it?

I am expecting to take far more than 2 weeks with my build.

Hi Ian.

Yes, I am very happy with it. Cuts straight in stoke as well as vertically. However, that was achieved by having good adjustment capability in the saw frame - the frame is all bolted construction, so that the forward and rear vertical struts can be adjusted in vertical angle, independently , allowing the blade to track perpendicularly to the saw vice, and in a vertical manner. The entire saw can also rotate a few degrees clock/anti-clock on the base to ensure a square cut as well. Welding up the blade frame would imply putting the adjustment mechanism in some other part of the machine somehow.

The Myfordboy saw has a very short stroke, which is ok when cutting large material, occupying a large length of the blade all the time. I have two crank pin position that are easily changed - 15 seconds or so - that give a mid length and a full length stroke - the mid length caters for material up to 80mm diameter, the full lenght for material to 40mm diameter.

I also first made a hydraulic lift mechanism to lift the blade on return - it worked very well, but I found by proper implementation of the crank center of rotation in vertical relation to the blade frame con-rod attachment position, it was very easy to get blade lift on the return stoke - the rising crank pin ( the 'big-end' on the forward return stroke pushes the frame up, and the falling crank pin on power stroke pulls the frame down, ie, the blade is pulled into the work.

Take a look from around 55sec into the video - you can see the frame up and down motion quite nicely - all the way into maybe 1.5 minutes into the video.

Hacksaw Video

Clive Foster said:

If you want a quick build might be worth looking into replacing the built up from hexagon bar slide system with one of the linear rail and bearing block systems that can be got quite inexpensively these days.

I had also hoped this would work since it would save some DIY pains - I made a test frame and gantry and it worked ok - was noisy - the little balls in the slide block did not like a 100 strokes/min at all; even 60/min was not nice..I had my doubts though, and that noise translated into ball failure after about 3 hours of running at 100 strokes/min - lubrication was a bit difficult as the slide block has a wiper to keep grit out of the balls, and it would wipe away most of any lube applied. The blocks and rails I used were SKF ( damn expensive!) , the rail is a 40mm wide 20mm high rail, and I used two long blocks - 75mm long each.

I tend to runthe saw at 80 to 120 strokes/min all the time - anything slower is frustrating!

Joe

 

EDIT - eliminating errant emoji's!

 

Edited By Joseph Noci 1 on 13/09/2019 07:15:41

Clive Foster13/09/2019 10:03:12
2254 forum posts
76 photos
Posted by Joseph Noci 1 on 13/09/2019 07:12:58:
Posted by Ian Thomson 2 on 12/09/2019 19:40:20:

Clive Foster said:

If you want a quick build might be worth looking into replacing the built up from hexagon bar slide system with one of the linear rail and bearing block systems that can be got quite inexpensively these days.

I had also hoped this would work since it would save some DIY pains - I made a test frame and gantry and it worked ok - was noisy - the little balls in the slide block did not like a 100 strokes/min at all; even 60/min was not nice..I had my doubts though, and that noise translated into ball failure after about 3 hours of running at 100 strokes/min - lubrication was a bit difficult as the slide block has a wiper to keep grit out of the balls, and it would wipe away most of any lube applied. The blocks and rails I used were SKF ( damn expensive!) , the rail is a 40mm wide 20mm high rail, and I used two long blocks - 75mm long each.

I tend to runthe saw at 80 to 120 strokes/min all the time - anything slower is frustrating!

Joe

 

Joe thanks for confirming my worry that the usual inexpensive ball bearing linear rail systems aren't up to handling the stroke speed needed. Plain bearing ones will be fine so I shall need to either find some or make my own from dry bearing wrapped bushes when (if) a project requiring a similar motion actually happens.

Concerning stroke speeds I tripped over a description of the Catra Hand Hacksaw Blade and Cutting Test Machine **LINK** . This is a PC controlled device made to test the cutting performance of hand hacksaw blades as specified in BS1919. It is a two speed machine with a stroke of just over 155 mm ( 6.1 inches) and runs at either 35 or 75 strokes per minute. Test time is said to be either 25 minutes in automatic mode or 40 minutes in manual. As its a test device the speed is clearly safe and won't burn up the blades even though they are clearly being worked hard.

Much more in line with Rapidor speeds which tend to be in the 60 to 100 strokes per minute region although some other breeds do run faster eg Denbigh Swiftcut. Proper power hacksaw blades are much tougher then repurposed hand ones too. Probably worth comparing with bandsaw blade speeds too. At these sizes, say 6" ± a bit cut length, its probably close enough to simply convert rpm into ft/min cutting speeds and be done with it. With so many variables getting to works OK is hardly a precise issue.

Thompson & Sarwar have a paper on power hacksaw machines in the Proceedings of the Fifteenth International Machine Tool Design and Research Conference which looks to have data on actual cutting performance, blade life and speeds but it seems to be subscription only.

There is a picture at the bottom of that Catra page showing the actual test machine. Its an old Rapidor saw poshed up, painted and fitted with round rail linear bearings instead of the standard square bars. Housing size suggest they are plain bearing ones.

Clive

Edited By Clive Foster on 13/09/2019 10:04:17

IRT24/05/2020 22:15:47
104 forum posts
32 photos

I did say more than 2 weeks didn't I?

After 7 months I have assembles the parts made so far.

It is starting to look a bit like a hacksaw now.

The motor and vice are not attached yet - just placed in position for the picture.

2.jpg

1.jpg

4.jpg3.jpg

 

Edited By IRT on 24/05/2020 22:17:54

oldvelo25/05/2020 01:55:07
218 forum posts
51 photos

Hi

This hacksaw has been in use for over ten years now with no problems. Hand hacksaw blades 18 TPI @ 50 to 95 strokes per minute with a rocking and oscillating cutting action that means that only a few teeth at a time in contact with the work.

Wobbly Hacksaw

Eric

Edited By oldvelo on 25/05/2020 01:57:02

Joseph Noci 125/05/2020 07:10:54
711 forum posts
917 photos

Looking Good IRT!

Do you have a VFD/3phase motor setup on the saw? If not, maybe the stroke/min may be a bit high with those pulleys? A (very) rough guess looks like about 8:1 ratio - If the motor is around 1400rpm, then 170 or so stroke/min is rather high. Even a 10:1 is still to high. Try for around 60s/min up to maybe 100s/min.

Joe

John Haine25/05/2020 09:36:38
3181 forum posts
172 photos

It's probably not very helpful but in the March/April 1994 issue of MEW my father described (alas without photos) a vertical power hacksaw he made built around two box-section plywood structures that telescoped. The material vice was on the top. I recall it was about 8" square and 24 high and used a standard hacksaw frame and blades. Its advantages were that the blade was swung back from the material at the end of the stroke and didn't re-contact it until on the cutting stroke, which greatly reduced blade wear; and of course it took up very little bench space. I think at some stage it broke when he was too old to fix it, and then disappeared when his house was cleared after he died. I remember he used it a lot as the vertical blade was very good for things like roughing out shapes for milling to finish size (vee blocks for example).

IRT27/06/2020 23:19:19
104 forum posts
32 photos

I finally finished the build today.

Now I just have to make it pretty.

5.jpg

6.jpg

It runs lovely and smoothly.

I will wait until the final assembly before making a cut with it at this will put a slot in the plate at the front.

not done it yet28/06/2020 08:26:00
4747 forum posts
16 photos

Looks like a job well done. Neat and fairly compact. Very much worth waiting for. I’m sure it will serve you well (and avoid ‘tennis elbow’ in old age! Less than a year for a project like this is perfectly acceptable for me.

The only downside (IMO), from videos I have seen, is that they seem to run at a rather frenetic rate - 240 strokes per minute.

The ETW design operated at just 90 strokes per minute. It uses a geared reduction drive, so no belt.

The toothed drive pulley perhaps slows it a bit? What is the motor size you have used? It looks BIG!

Joseph Noci 128/06/2020 09:47:10
711 forum posts
917 photos
Posted by IRT on 27/06/2020 23:19:19:

I finally finished the build today.

Now I just have to make it pretty.

That looks very nice! Very compact and certainly a lot lighter than mine! Please post a link to a video of it doing its thing..

Well done.

Joe

edit : won't that rearward protruding part of the blade smack the motor? Maybe you just have not cut it short yet..

Edited By Joseph Noci 1 on 28/06/2020 09:48:32

not done it yet28/06/2020 11:14:58
4747 forum posts
16 photos
Posted by Joseph Noci 1 on 28/06/2020 09:47:10

...

edit : won't that rearward protruding part of the blade smack the motor? Maybe you just have not cut it short yet..

Edited By Joseph Noci 1 on 28/06/2020 09:48:32

It’s already at the rearmost part of its stroke, Joe.

IRT28/06/2020 11:22:40
104 forum posts
32 photos

The motor is smaller than the original used. The plans describe using a 1/3hp motor, but state a smaller one would provide plenty of power.

This one is 1/4hp, 1400rpm. with the gearing about 6.25:1 this does indeed have a theoretical speed of about 220rpm.

Surprisingly, it does not appear scary fast - at least when only cutting fresh air.

I have not worked out what cutting speed this equates to.

Clearance is not an issue. It is a way off the motor. It does get close to the crank - but again nothing to worry about.

9 months elapsed time so far. I did have a break of a couple of months when the garage was too cold.

It is my first 'proper' project, involving milling, turning, silver soldering, casting, welding, etc. I have learnt a lot.

I will put a video up once it is finished, but I need some better weather before I can paint it.

Joseph Noci 128/06/2020 13:36:30
711 forum posts
917 photos
Posted by not done it yet on 28/06/2020 11:14:58:
Posted by Joseph Noci 1 on 28/06/2020 09:47:10

...

edit : won't that rearward protruding part of the blade smack the motor? Maybe you just have not cut it short yet..

Edited By Joseph Noci 1 on 28/06/2020 09:48:32

It’s already at the rearmost part of its stroke, Joe.

Moral is - open eyes, then engage brain, before opening mouth or typing...!

Joe

larry phelan 129/06/2020 10:08:43
769 forum posts
14 photos

Might sound like a silly question, but why bother with a saw which uses only some of its teeth when you could have a bandsaw using all its teeth ?frown

IRT30/06/2020 17:47:05
104 forum posts
32 photos

The big driving force for me in making the decision is space. This will hang on a wall. I agree, a bandsaw would be far more effective, but I just can't fit one in.

I was also looking for an interesting project that may be useful in the future.

I do have concerns about how well it will actually cut using only part of the blade. Other people who have made it seem to be pleased with the performance. I will report back in a few weeks once it is finished.

One final advantage I can think of, is that the hacksaw can be left to perform its task with no supervision. It doesn't matter if it takes 10 times as long to cut a steel bar, because I can be doing something else.

IRT11/07/2020 10:05:47
104 forum posts
32 photos

So much for making it pretty.

I know as soon as I pick up a paint brush or aerosol things are going to go downhill. This morning was no exception.

I have runs, bubbles, and insufficient coverage in the space of a few inches.

The damage has been limited as I have run out of paint.

I suppose trying to spray outside in a breeze is asking for problems.

So now I have to decide: do I rub it all down only to make the same mistakes and use up expensive paint, or do I accept that it is only a tool that is going to get bashed about so cut my losses and leave it?

I have a small compressor - maybe I could get a cheap air gun and try that - or maybe try applying it with a brush (that always goes badly wrong).

I will let it dry for a couple of days before I make up my mind.

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