Chop saw

I'm building a chop saw for metal and I was thinking to share here the progress. It is going to use discs up to 350mm. I want to be very solid. I have this 3-phase motor for it:

Today I started to make a large pin. It will hold together the base of the saw and the mobile part (motor + disc). So I'm making some kind of hinge. I have many 10mm thick 55x100mm metal plates that I'm going to use them for this. Bellow is a quick drawing.

I wanted to turn the pin between centers. But I don't want to remove the chuck. So I cheated and I made a center and hold it in the chuck. As long as I don't remove it the concentricity should be perfect.

My lathe is not aligned so I used a precision rod to measure the error. After adjusting the tailstock I reduced the error to <10 microns.

I don't have a dog. So I welded a small piece of flat steel to one end of the bar. I'll remove it later.

After cutting around 1mm in total I discovered to my surprise that the diameter of the bar is 0.2mm larger at the right end! So the tailstock is seriously misaligned. There was something wrong with my first attempt to aligned the centers. I moved the tailstock with 0.1mm closer to me. And after another 0.3mm cut the diameter difference at the ends dropped to 7 microns! So far so good.

Edited By Sonic Escape on 17/06/2023 20:20:11

I enjoy progress threads like this. When I can't get out to my workshop myself I machine vicariously through others! Thank you.

Interesting project.

That's a perfectly valid way that: a temporary centre turned in situ. Hemingway suggests that for using the boring-bars made as one of their kits.

I'm not sure I'd have welded that lug on though. I'd be worried about distorting the bar. I have improvised dogs in the past by drilling and tapping the side of an old nut or slice of thick-walled tube to take a bolt that acts as both grip (with a surface-protecting pad) and driving-arm. For an application like yours I'd have welded the lug to the ring, and tapped through the extra thickness of steel for the grip screw.

The problem, with such welding, arises when you come to reversing the part between centres for further machining.

Better, IMO, to fabricate a drive dog than mess around as you have done. A piece of flat bar, a bolt and nut as a drive and a pinch bolt (a slot cut to allow some pinch) or grub screw to affix the drive dog to the part being machined. Maybe spot drill the workpiece for the grub screw?

What power is your motor for your chop ‘grinder’?  350mm discs will need a fair amount of power.  Also be aware of disc speed limitations - you will need different speeds for different diameter discs

Edited By not done it yet on 18/06/2023 08:53:41

Nigel Graham 2
Distorting the bar by welding is not an issue because anyway I will turn it later. I also thought initially about a more elaborated method to make a dog. But welding produced a more rigid result. Even this "dog" was bend a little in the end.

not done it yet
True, but I don't have to reverse the part. I want only to decrease the diameter at both ends with a chisel style tool. The motor has 1.5kW S1. Up to 1.8kW @ 460V. I saw that some chop saws have motors up to 3kW. But I will give this one a try. I will use the VFD from the lathe, so I can adjust very easy the speed. The motor has 1400RPM. So with a 1:1 belt drive I should have the maximum speed recommended for carbide discs.

Today I finished the work on the pin. I decrease the diameter by ~10mm at both ends. I made an interesting discovery. If I'm using oil, the cutting tool is rubbing the metal, accumulate tension and then suddenly starts to cut a large chunk of metal. You can see this at 0.42:

I also killed the dog because its job was done.

Next I wanted to made the holes for the pin in the 10mm plates. I fixed the plate in the chuck like this. And turned it very slow, 70-80rpm maybe. I also avoided to stay too close to it.

I discovered that I can't drill holes larger than 10mm. I need 1mm more to fit the boring tool inside to start to enlarge the hole. I should have a 12mm drill but I can't find it. I have also 16mm drill but I lost the ER32 collet for that size! And my giant MT3 drill is 2mm too large. Bad luck today. Time to do some shopping.

Here is the proof that I need a chop saw. This cut was supposed to be made along the line, but I couldn't see it well because of the sparks ...

One last thing, this Milwaukee discs are cutting much faster that anything I tried before. It looks like a good brand.

Edited By Sonic Escape on 18/06/2023 20:52:01

When you mount work in a 3-jaw like that, there's only one jaw 'driving' the workpiece round (the one at '5 o'clock' ).

If you use a single point tool to make an aggressive cut, say if cutting a rebate from the centre out, when that jaw gets to '10 o'clock', the cutting forces will be pushing it away from it's partner at '6 o'clock'', whilst the jaw on the short side will actually be trying to eject it.. ..you can see what could happen.. ..be careful..

Sometimes for work like that you can turn just one of the jaws in a 4-Jaw round to hold the 'long' end; maybe someone has a picture?

Edited By DiogenesII on 19/06/2023 07:37:56

Edited By DiogenesII on 19/06/2023 07:38:18

Or you can hold the plate in a similar way in the four jaw chuck and it will be more stable.

I think you would have been better off to turn the steps on the ends with a normal turning tool. What you are using in the videos is parting/grooving tool plunged straight in. Less than ideal and as you found, prone to erratic cutting. It is not really designed for that sort of use. But it got the job done so at the end of the day, that is all that matters.

Yes Milwaukee is a good brand for power tools and cutting discs etc as you have found. They are widely used here on construction site work which is notoriously rough duty. But not cheap!

The workpiece feels very secured in the chuck and I'm using a low speed. Also I'm standing more on the right side than usually when working with this plates.

As for the aggressive cut, I'm going to use this arrangement. I would be happy if I could make a cut at all
There are adapters for this boring tools but I didn't figured out which type is required by my tool.

Here Milwaukee discs are in the same price range with Bosch and others. Around half a pound. What is really expensive is a Cubitron II from 3M. I wonder how that one is cutting because it is six times more expensive!

Also I ordered this thing. I think it is called annular cuter. On the lathe I'll make only a 4-6mm hole to mark the right spot and then I'll move the plate on the press drill and cut a 22mm hole with that special drill. That will be large enough to insert the boring tool to make it larger.

Edited By Sonic Escape on 19/06/2023 16:18:15

I finished boring a hole in the 10mm plate. Despite all my efforts I managed to make it some 0.18mm larger. I was making very fine cuts, I don't know how this happened. I think I need a telescopic gage. Now when I put the bar inside it has a small play and I don't like it.

So I consider to move to plan B. I think a taper will make the design less sensitive to exact dimensions.

Today I made a tapered hole. By modifying the existing one. I choose 30°.

And I made a similar modification to the pin. Now as long as they are pressed one against the other they are fitting much better. There is no play.

I didn't turned the pin between ​​​​​​centers this time. I don't think it matters. I didn't wanted to weld again a piece of metal to turn the bar. Maybe is time to make a reusable dog.

Big motor and saw blade for flimsy construction.

Regards Ian.

Hmm ... what is flimsy?

Today I finished the second plate. Also tapered. This annular cutter is very good. I used only 200rpm and light pressure but it is cutting very well.

And this is the result. I will weld two flat plates to each plate that is supporting the pin. So I could use screws to connect them to the base of the saw. In this way I have a way to fix possible misalignments.

A good step forwards having sorted the initial problem!

I'm thinking how to make the arbor for the saw. It will have more or less the same length as the pin that I already made. It will be supported by two 35mm bearings. At one end the diameter will be reduced to 20mm for the disc. I want to use also 1" discs so I will made a sleeve.

The motor has a 60mm poly-V type pulley. I don't want to replace it because I don't have a tool to remove it. I need a similar pulley for the arbor. But the only one I found so far costs more than 100 euro. So I want to make one. Is there a problem if I make it from HDPE? This would be my first choice for material. The second is aluminum.

Today I bought 2 bearings. I choose a type that has a taper inside. I don't know how is called but I liked it more that the other ones where you have to use a hammer to put the bearing in place. That black nut is puling a slotted sleeve that is holding the arbor.

It is also a self aligning model that it suppose to work up to 8000RPM. But at home when I opened the box I started to be a little suspicious. The balls are ringing and feel loose. I think it will be noisy. Also it looks like you could almost disassemble it if you pull the rings a little harder. I don't know it this is the best choice.

Also I welded the horizontal support plates for the pin

I found a picture with a chop saw that look similar in many ways with what I want to build. Mine will not be so ugly, of course 

Edited By Sonic Escape on 26/06/2023 21:10:39

Edited By Sonic Escape on 26/06/2023 21:12:28

Edited By Sonic Escape on 26/06/2023 21:13:25

Last days I made some progress on the chop saw arbor. First I made a poor man's dog. I need it to turn a 40mm bar.

Then I cut the bar from 40mm to 35mm. This is the diameter of the pillow block bearings. I also cut one end to 1" diameter for the pulley. At the end of the video there is the everything assembled.

I want to make a 10mm length thread on the arbor. M22x1.5. The thread will be used by a 10mm thick disc that will hold one side of the blade. I have a die and I made a simple die holder for it. By chance I found a short pipe with thick walls that was just the right size.

I made a small cut on the wall and I inserted a piece of flat steel to lock the die.

While welding I put between the die and the flat steel a piece of Aluminium from a Pepsi can. So I could remove the die later.

I added also two handles and tomorrow I'll give it a try:

Put the metal plate into the vice jaws along the line of the cut

and cut with the grinder disc skimming along on top of the vice jaws

Voilla. A perfect straight cut every time

Edited By Ady1 on 23/07/2023 10:17:44

This Sunday I went to a bazar and I found an interesting tap holder. It was exactly what I needed. I made an MM22x1.5 thread on a 10mm thick steel disc. This disc will hold one side of the blade.

The using the die holder that I just built I made a matching thread on the saw spindle.

Everything went fine. But I didn't realized that the tap or die are not self aligning. Especially if the thread is not to long. So the result is this:

Yes, I guess that should work. I found also another method. I make a light cut along the whole length. Just 0.5-1mm deep. This is easy to make it straight. Then the cutting disc will not slip outside of this line. Even if you can't see the line because of the sparks you can still feel it if you don't press to hard the grinder.