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Small saw. Proxxon or something else

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Martin Kyte22/04/2021 20:34:48
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Posted by John Smith 47 on 22/04/2021 16:50:29:

**LINK**
"The 28020 is a Tungsten tipped Saw Blade with high-alloy special steel"

Given that it is tipped with Tungsten, how come it can't cut mild steel? I get that it can't but I am curious to know why it can't. I was thinking that if we could slow down the RPM, and increase the torque of the motor (e.g. by having a higher wattage motor running more slowly) maybe that would help

Likewise I am also curious that solid carbide discs are no better.

Either way for thin metal sheet (e.g. 0.1mm) the easiest way to cut it and maintain flatness still seems to be a very high speed disk.


OK, just how mad is this suggestion?
Go for something mass-product & much more powerful and find a way to do precise grinding cuts.

e.g. Bosch GTS635-216

**LINK**

Cost: £335.99
Power: 1600watts - a surplus of power
Speed: 5,500 RPM - pretty very fast for 21cm
Weight: 22Kg - not impossible
Incline: 0 to 45degrees
Saw blade diam: 216 mm
Bore: 30 mm

I just need to find some very thin (1mm? 2mm?) abrasive cutting disks that are 216x30mm.
[I ran out of time googling but surely they exist!]

But even if I have to settle for quite wide cuts, at least I would get my straight cuts... through steel.

J

The gullets on the TCT circular blade are huge. I would suggest that the least worst case would be that the material stalls the saw and the worst case that it throws the material back at the operator. If you look at an Evolution Chop saw blade which is designed to cut metals the gullets have an anti kickback profile which limits the depth of cut.

regards Martin

John Smith 4722/04/2021 20:44:58
271 forum posts
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Posted by Michael Gilligan on 22/04/2021 17:27:32:
Posted by John Smith 47 on 22/04/2021 16:50:29:

**LINK**
"The 28020 is a Tungsten tipped Saw Blade with high-alloy special steel"

Given that it is tipped with Tungsten, how come it can't cut mild steel? I get that it can't but I am curious to know why it can't. I was thinking that if we could slow down the RPM, and increase the torque of the motor (e.g. by having a higher wattage motor running more slowly) maybe that would help

Likewise I am also curious that solid carbide discs are no better.

.

.

The blade is intended for an underpowered machine with an inadequate spindle

Please see Peter’s post and my response, on page 1

The blades could almost certainly do your job: if suitably supported and adequately powered at an appropriate speed.

... but Proxxon needs to inform you in the context of its machines.

 

MichaelG.


CUTTING WITH BLADES
OK please can you help me out here. Use of blades means calculating the cutting speed (i.e. "Vc" ).

1) What is the correct range of cutting speeds for mild steel? A what would be a reasonable margin for error on this?

I looked it up on Wikipedia and found the suggested cutting speeds range from "3 to 38 metres/minute" for mild steel - but I believe some people are challenging this(?)
Aluminium is: "122 to 305 m/min" cutting speed.
Wood is: "183 to 305"


2) And how can I calculate the correct RPM vs diametre in order to get this cutting speed?

I believe that the correct equation is:

Cutting Speed (called "Vc", in metres per minute) = (Pi x Diam (in mm) x RPM) /1000 ... yes?
i.e. Vc = (3.141592 x Diam x RPM)/1000


Example A.
In round numbers, supposing we had a disk of 100mm diametre running at 5,000RPM, plugging the numbers in we get:
Vc = (3.14 x 100 x 5,000 )/1000 ==> 1,571 ==> call it 1,500 m/min - which is more like 100 times what we want for steel, no?

Example B.
My little 22mm abrasive cutting disk cuts well at 20,000 rmp, but I notice that it doesn't seem to cut well at c. half that speed
Vc = (3.14 x 22mm x 20,000rpm)/1000 ==> 1,382 ==> call it 1,300 m/min

Example C.
Proxxon FET Table saw - large 80mm disc:
Vc = (3.141592 x 80mm x 7000rpm)/1000 ==> 1,759 ==> call it 1,700 m/min

Example D.
Proxxon FET Table saw - small 50mm disc:
Vc = (3.141592 x 50mm x 7000rpm)/1000 ==> call it 1,100 m/min

Example E.
Rutland Mini Saw
80mm disc, 6800 rpm ==> c. 1,700 m/min
80mm disc, 4400 rpm ==> c. 1,100 m/min

Example F.
Bosch GTS635-216
216mm disk, 5,500 rpm ==> c. 4,600m/min
(but can I find a 1mm thick disk? If not could I tolerate an unnecessarily wide cut?)

Conclusion:
These disks are all spinning FAR too fast, even for Aluminium and wood they are way too fast!
For mild steel presumably what is needed is much slower, but also more torque

CUTTING WITH ABRASIVE DISC
A 1mm wide cut would be a reasonable target. Yes things can get very hot but at least thin plates don't get bent where the don't get hot.

J


PS What about a reciprocating 'jigsaw' built into a table-top?
e.g. Rockwell BladeRunner X2 - is dirt cheap c. £170 (and does at least claim to cut steel!)

**LINK**

Let's be honest it's way too cheap to be of good build quality (sounded noisy in a youtube review) and it's USA voltage so I would need to get a voltage converter too. But it got good reviews on eBay (4.6* from 278 reviews).

 

Edited By John Smith 47 on 22/04/2021 20:45:24

Edited By John Smith 47 on 22/04/2021 20:45:47

Edited By John Smith 47 on 22/04/2021 20:46:07

JasonB22/04/2021 20:51:29
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You don't say what you are cutting with HSS, carbide and Abrasive discs will all have different cutting speeds and you have been considering them all in this thread.

Ian P22/04/2021 20:58:41
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As I understand it the OP want to cut 0.1mm/0.004" sheet steel (into narrow strips?)

How narrow? how long? what kind of steel is this? how good does the cut edge need to be? lots of questions come to my mind but if I had to cut (what sounds like shimstock) I would never had thought of sawing.

Sawing such thin material is in watchmaking territory, it certainly can be done but the work has to be very well supported and doing this on a circular saw type machine where the blade comes through a slot in the table the edge of the slot is going to be further from the side of the blade than the material thickness.

For one-off or small quantity it might be best to bond the steel to a sacrificial plate (brass, steel or even a sheet of Formica) and use a mill or router to create the outline before separating the parts.

Other possible methods of making parts out of thin material include, laser or water-jet cutting or etching.

Ian P

John Smith 4722/04/2021 21:13:04
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Posted by Pete. on 22/04/2021 18:54:18:
Posted by John Smith 47 on 21/04/2021 12:15:56:

@Pete - I need the metal to stay absolutely flat after it has been cut.
In my experience sheers never seem to achieve this.

Rather than endless what ifs, I thought I'd demonstrate what I said.

A simple table on my bench shear before I had machine tools at home, it would be made with dowels at various angles now.

Bench shear 1

Bench shear 2

@Pete to get clear you are saying that even a huge guillotine puts a curve into ONE side of 1mm thick mild steel sheet, but the other side stays dead flat, yes?

To my mind that is just a nightmare, because you end up will loads of bent mild steel that you cant use for anything else unless you find a way to bend if flat again. And that means huge bulky rollers as well as a high bulky guillotine.

I think all my problem would be solved by:

A) a small abrasion-type cutting disk that is 1mm thick, that is buried into a table in a circular saw table
type of configuration.

B) for slightly thicker steels, a slow turning circular saw (or band saw?) that has a very high torque should do the job.


Regarding Proxxon as a brand, I find myself deeply conflicted. I have some of their stuff and in general it is reasonably good, but i) the prices are extremely high and ii) the build quality is sometimes very good but the next minute it is absolutely woeful, for no good reason. I mean certain things rattle badly that damned well shouldn't rattle at all.

Bottom line: Proxxon stuff is all pretty expensive and although much of their stuff is great, but you can't RELY on the brand to be great.

This make them sometimes feel like toys for amateurs even though some of their stuff IS pretty darned good. Frankly they just need a big new management shake-up and proper quality control... and a few spindles that run true and they would be absolutely brilliant.



John Smith 4722/04/2021 21:17:27
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JasonB
In my defence, see 3rd paragraph of my intial post:
"But will it be able to cut/grind mild steel and stainless steel?"

And most of it will be c. 1mm thick sheet. Recently I had to cut some that was 0.1mm thick too, so it would be nice to combine both. 

Wait, do abrasive discs care about cutting speed? It seems to me that the faster the spin the better the sparks, fly off taking the heated material with them. Am I missing something?

@Ian P - Regarding length of cut, it varies - ideally at least 10cm.
Yes, using a sacrificial material is an option, but it is time consuming and messy, so I was broadly hoping to avoid doing much of that.

Recap: I was very struck by just how well a thin abrasive cutting disk (38mm x1mm @ 10,000 to 20,000 rpm) cut through both my 1mm thick steel AND my 0.1mm thick steel. It was fast and it left the sheets absolutely flat (once de-burred). Also, FWIW, at larger scale (according to various youtube videos) it seems huge cutting disks are the way to cut though steel FAST with angle-grinders etc. 

My problem is that they can't do LONG, accurate cuts - but 'obviously' (to me at least!) you could if the blade was buried within a table in a circular saw table type of configuration.

Unfortunately (as far as I can see) the world doesn't seem to have made any circular saw tables that have 1mm thick abrasive cutting disks!

Edited By John Smith 47 on 22/04/2021 21:34:13

Edited By John Smith 47 on 22/04/2021 21:36:15

speelwerk22/04/2021 21:46:35
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Perhaps not possible with stainless (never tried) but 0.1 mm brass cuts easily with a Stanley knife along a ruler. Niko.

John Smith 4722/04/2021 23:00:34
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Posted by speelwerk on 22/04/2021 21:46:35:

Perhaps not possible with stainless (never tried) but 0.1 mm brass cuts easily with a Stanley knife along a ruler. Niko.

I tried with a knife on a cutting matt but what resoluted was not longer flat and got bent near the edges. The problem is that 0.1mm is quite easily bent.

To get clear, I need a result that its more or less "optically flat"! i.e. It is not bent around the edges, and when I sand it down with super-fine wet & dry the sanding goes right to the edges of the cut.

Fwiw, I was cutting a 10 x 5mm piece of 0.1mm mild steel. I suppose if you cut it against something that was very rigid, but not quite rigid-enough to blunten your blade - maybe a very rigid cutting mat that you don't mind damaging, then you might get away with it (??)

Pete.22/04/2021 23:27:59
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As I said before, cut it oversize using a method that doesn't bend it, angle grinder slitting disc, Bandsaw, anyway that pleases you, personally I'd use my makita 18v sheet metal shear as it doesn't distort the sheet on either side.

Then with the fence set to exactly 90° on my bench shear, trim one edge, place trimmed edge against rear fence, trim second edge, repeat, you now have a square with straight cuts and 90° corners as accurately as you set the fence.

Makita shear 2

Makita shear 1

speelwerk23/04/2021 00:01:07
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I just cut it on the workbench which is made out of melamine board and changed every year or so when it has to many (cut) marks. With a sharp knife it stays straigth and leaves almost no bur. Niko.

JasonB23/04/2021 07:14:49
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John I did read what you wanted to cut and have mentioned yoyr 16 x 13 plates to give people an idea of sizes.

You asked "what is the cutting speed range for steel" and I asked with what you were going to be cutting with as each cutter will have a different cutting speed.

I gave a speed in your other thread and queried those you got from Wiki

As a rule of thumb if using HSS then 30m/min, Carbide tipped or solid tooling 100m/min and abrasive discs 3-4000m/min all could be +/-20

From this and your example calculations it's easy to see that all these saws are really designed for wood as the speeds are optimised for that and too fast for optimal cutting of metal with HSS or TCT blades or a bit too slow for optimal cutting with Abrasive discs

As a simple example that saw blade I show in the mill when cutting steel would be going at about 100rpm if cutting steel. A similar size 1mm cutting disc in my small angle grinder would be running at 11,000rpm. Now maybe you can see why I asked what cutting materials was being used as it affects the cutting speed

Stuart Munro 123/04/2021 07:27:18
108 forum posts
Posted by John Smith 47 on 22/04/2021 21:13:04:


Regarding Proxxon as a brand, I find myself deeply conflicted. I have some of their stuff and in general it is reasonably good, but i) the prices are extremely high and ii) the build quality is sometimes very good but the next minute it is absolutely woeful, for no good reason. I mean certain things rattle badly that damned well shouldn't rattle at all.

Bottom line: Proxxon stuff is all pretty expensive and although much of their stuff is great, but you can't RELY on the brand to be great.

This make them sometimes feel like toys for amateurs even though some of their stuff IS pretty darned good. Frankly they just need a big new management shake-up and proper quality control... and a few spindles that run true and they would be absolutely brilliant.


Joihn, I have to agree re Proxxon. I have one of the FET table saws discussed in this thread; its generally very good and can be adjusted to about 0.1mm BUT the fence appears to be about 0.5mm out along its length but the BLADE is what is not at 90 degrees to the table. I make do by setting the fence parallel to the blade but for a tool of this price this should not happen.

Stuart

Stuart Munro 123/04/2021 07:43:59
108 forum posts

p.s This is why I'm attracted to the Byrnes Table Saw - by all accounts the Rolls Royce of wood modellers table saws but coming in a £550 - £600 landed in the UK.....

Stuart Munro 123/04/2021 07:45:30
108 forum posts

pps - now that I know that it has blades to cut Brass sheet and aluminium sheet it may become a realistic option as a multi material saw. Off to se the minister of home finance.

Michael Gilligan23/04/2021 08:47:11
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Posted by John Smith 47 on 22/04/2021 23:00:34:

.


To get clear, I need a result that its more or less "optically flat"!

.

dont know Is that another of your ambitious ‘specifications’ [ like EXACTLY 45° ] ?

... or are you serious ?

I can find no credible definition of “more or less” ... but to have any hope of knowing what you have achieved, you will need to measure flatness; so you might find this helpful: **LINK**

https://www.kemet.co.uk/blog/lapping/how-to-measure-flatness-technical-article

MichaelG.

Dave S23/04/2021 12:42:00
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Seems to me if you had a small mill, somewhat like a sherline 5000, where the head can be set over at an angle then you could just use a slitting saw on an arbor.

As a bonus that machine could also do all sorts of milling things, and probably make precision V blocks with 90 degree included angles as well

Dave

John Smith 4723/04/2021 14:46:44
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@Pete - I know that there will always be a little bit of finishing required.
For 1mm I just use a fine hand file and/or some fine wet & dry glued onto a flat piece of MDF.

But what's the thinnest sheet you have cut this way and had it come out without being bent?

I am working with magnets and even the slighest bed in the steel sheet is completely unacceptable. These bends only become evident when you try to sand/polish the steel.

Yes I tied a nibber - manual one used extremely carefully - and the results were completely unacceptable.


@speelwerk - Melamine sounds like a good compromise. Do you mean like a kitchen sideboard panel? (I have some but it has a mat rather than dead-flat finish).


@JasonB
> "each cutter will have a different cutting speed"

Nightmare! In my experience life is to short to get cutting speeds exactly right.

> As a rule of thumb if using HSS then 30m/min, Carbide tipped or solid
> tooling 100m/min and abrasive discs 3-4000m/min all could be +/-20
Thanks - that's helpful.

My little abrasive cutting disk cuts extremely well at 1,300RPM.

> From this and your example calculations it's easy to see that all
> these saws are really designed for wood as the speeds are optimised for that
But are they really?
I thought the cutting speed for wood was "183 to 305" m/min!

@Stuart - Q.E.D. !

Byrnes Table Saw for £600 not completely impossible... It does look beautifully made! But even for that money you're not getting a tilting table, it's fixed speed (3450 rpm ). There is an optional tilt table (although I can't see how that works... I think you can only just the width of a chamfer rather than cut a whole sheet using a tilted cutting angle)

@Michael Gilligan...
> Is that another of your ambitious ‘specifications’ [ like EXACTLY 45° ] ?
> or are you serious ?
That is somewhat unfair. As we all know, there is no such thing as "exactly" any dimension within a workshop and I was speaking loosely, not pedantially and I meant "as close to exactly 45° as one can reasonably hope to obtain in a home workshop without undue time, effort and pain..." moreover I did subsequently clarify that I needed my 45° chamfer to at least be within 1 to 1.5 degrees

The wavelength of light is about 0.5 microns so no, I don't literally mean within the wavelenght of light, I meant that when you polish the surface there is no obvious bending in the plate near the cut that has been caused by the cutting process.

Like I pointed out for very thin sheets of steel sawing is not an option.

When I say "optically flat" again I mean that when you polish the darned thing up with a very find emery cloth, that the reflection of the surface still LOOKS to be absolutely flat. To be pedantic maybe I should have said that the surface needs to be "absolutely as flat as one can reasonably hope to obtain in a home workshop and by looking at the reflection of the surface it is not obvious bent". Happy? Or maybe "accurate to within say better than 25 microns/1 thousandth of an inch" would have been better?


@Dave S - When I have a bit more time, a bit more space and a bit more money... yes, absolutely. Right now I just can't quite afford that sort of money... (GBP 1000 to 1500 delivered to UK) but I do hear you. And I shall ponder further.

JasonB23/04/2021 15:00:40
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Posted by John Smith 47 on 23/04/2021 14:46:44:


I thought the cutting speed for wood was "183 to 305" m/min!

My woodcutting saws give a speed of just over 3,000m/min that's 250mm blade at 4000rpm.

Cost of the Sherline is not so bad as it will do the work of a separate saw, also do the work of an accurate drill that you were recently asking about and also all the other things a mill can do in one machine rather than several.

John Smith 4723/04/2021 15:58:36
271 forum posts
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@Jason B
> also do the work of an accurate drill
Except that it doesn't have a quill, so presumably it's kinda painful to get the swarf out as you drill, no?

@Stuart Munro 1
RE Byrnes Table Saw

I have just discovered

1. The basic saw weighs 29 lbs (13.1Kg)
==> That IS pretty heavy... but it is SO beautiful that I would forgive it!

2. The motor is a capacitor start motor 1/3 HP (250watts) 3450 rpm.
"It cannot be slowed down or sped up. It’s not designed to cut steel"

Discs seem to be 3" or 4". ==> and so cutting speed will be way too slow for grinding.

So there you have it. Lovely bit of kit but no use to me.

Michael Gilligan23/04/2021 16:26:18
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Posted by John Smith 47 on 23/04/2021 14:46:44:

.

@Michael Gilligan...

[…]

Happy?

.

In a word ... No

But it is not my remit to check your specifications,

so I can retire quietly from the discussion.

MichaelG.

 

Edited By Michael Gilligan on 23/04/2021 16:27:05

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