I need to cut chamfers into x64 pieces of mild steel - any advice?

That's very helpful - thank you. One more question, what speed should I be using if I do use a Proxxon MF70 (which seems to spin at 5,000 to 20,000 rpm, albeit with (if memory serves) just a 100watt motor, so presumably the ability to generate a lot of heat but without very much torque...)

Btw, it turns out the burrs are all the same price between 4mm and 8mm. Which would you advise me to use?

J

John, diamond stones are intended for hard materials, when you use them it creates fine particles that form a slurry with the lapping fluid, this washes away.

When you use soft mild steel, it gums up the diamond stone, this is most probably why you've noticed it performing less well in a very short space of time.

I have skipped through this thread rather but if I have the gist of it correct then maybe this machine currently for sale on the Home Workshop **LINK**site might serve:

For Sale: Gravograph bevelling machine

Mon 6th Sep '21

Advert ID: 40428

Tools & Parts (Small tooling)
Used (Correct working)

Details:
A high speed bevelling machine for bevelling edges of thin sheet material especially plastics and alli for engraving etc. Uses standard ¹/₈" diameter Gravograph cutters. 230V AC model.
Collection welcome, or will courier

William.

Many thanks for the interesting suggestion, William  

Yes, I did see that product. My thoughts are:

- I couldn't find much about the "Gravograph bevelling machine" on line, so I am assuming that it is quite old and broadly unsupported.

- I didn't feel that I completely understand the thing as I couldn't really see how exactly it works, nor what sort of adjustments can be made and what sort of cutting tools it uses.

- For now I would like to invest in more general-purpose equipment.

- However I think it's just the sort of thing that would be very useful if/when we go into small-scale product.

Meanwhile I am buying some stuff and shall revert after I have done some experiments with it.

Cheers

J

Edited By John Smith 47 on 07/09/2021 16:35:53

Video at **LINK**

Basically it uses a pointed engraving-style "D bit" with a 90 degree point. This is rotating in a recess inn the base which has a fence machined into it. You hold the material to be cut against the fence and push it past the cutter which mills the edge. As the material is hand held and fingers are close to the cutter you'd need to be very careful especially cutting steel where the cutting forces will be much larger than the engraving plastic shown. But basically a variant on the "milling with a mitred cutter" approach.

For production I do suggest that you consult on the best manufacturing approach for this component - which may involve a re-design.

Good to know.

IME, one large problem is that when you first start using it, one is clearly loosening off some of the larger individual diamonds that are less well bonded to the whetstone. These can then cause quite a large problem by causing deep individual scratches in the part that are hard to remove.

To be honest, in its current state I am used to it and it is certainly getting no worse and it still broadly works fine for me as it is, even though a distinct degree of skill is required to make sure you don't cut off too much material and to make sure that the chamfer is at 90° to the sides.

That said, maybe I need to sharpen some carving knives that are made from a harder steel in order to bring the whetstone back to life!?

PS I have noticed that sometimes the steel can bite rather hard into the abrading surface, and I was worried that if I was TOO aggressive with it, that I would rub off all/most of the diamonds. However from what you say, maybe the opposite is true and I need to be much more aggressive with it and use parts made from harder materials, no?
 

Edited By John Smith 47 on 07/09/2021 16:50:49

The slowest speed available, and with plenty of good lube such as Rocol RTD.

Yes, the price of all of them at Cookson is equally scandalous. HS Walsh would be a better source. To save money and to keep the speed down at the cutting edge I'd buy/use the 4mm ones.

If you do choose the Proxxon route with these burrs you're going to need to get on top of several things:

1. As the metal is very thin at 1mm you're going to have to have very little excess protruding from the top of the vice [yes, you'll need a vice] if you want to avoid chatter.

2. The burrs have fairly long shanks - too long, frankly, to give the required stiffness at the cutting end when held in the standard Proxxon collet. The solution is to cut the shank short to minimize stick-out.

3. You're going to need some way of clocking in your vice so that its jaws are perfectly parallel with long edge of the table. Once you've achieved this you'll be able to cut the chamfer on a long piece all in one go and cut it into sections of the desired length afterwards. For long runs I tend to use a cordless drill on the nut on the end of the x axis as a powerfeed.

The Proxon Mill is around £350 the Gravograph device is £150 + carriage. The OP suggested he didn't wish to acquire equipment which would have no further use after completing the exercise. The Proxon depending on future intentions may be of no further use as it is only intended for light use on small components and £200 more expensive! The Gravograph machine would appear to be exactly what is required and the Proxon a compromise. If the project is of prime importance buy the Gravograph, job done.

Robert Butler

Hello All

OK, this is going to be embarrassing as I have now bought all manner of the above tooling!

TBH, I have taken so much heat from certain contributors questioning my motivations, my aptitude, my skill levels... and some seemingly taking offence if I don't acknowledge and execute the advice of each and every contributor... not that I get my self-esteem from strangers, but it IS kind of tedious to read some of the sniping ... so with all due respect, I shall draw a light veil over exactly what I have now bought.

However I shall get back with some photos once I have got some results. Although fwiw, most of the kit has not yet actually arrived in any case.

J

PS If nothing else I should have a good set of tools when this is all over!

You can never have too many tools!

Tony

Yup. ...And you can never have a large enough workshop in which to store 'em!

J

UPDATE:

1. I tried the Proxxon MF70 Micro Milling machine with the tool with the 45° cutting edge
("Busch Burr Stone Setting 8.0mm"


Although yes, it DOES work on my 1mm thick steels, it's a struggle. I set the speed to its minimum (5000rmp). It takes about 5 passes and it makes rather a mess of the job. Making it work harder, can certainly slow down the cutting speed but it doesn't improve the quality of the cut and doesn't really speed anything up.
[Passing comment: It feels odd not getting any feedback for how much strain the machine is taking, other than sound... plus a slight flexing!]

2. I also bought that cheap disk + belt sander from Aldi (Ferrex), partly because I found a couple of favourable reviews.




It's huge beast of a thing... much larger than I really wanted but it's certainly cheap (£93 delivered).

But I have to say the build quality is appalling! The hole for the rod that supports the worktable rod was way, WAY off being parallel to the disk. So far off in fact that it was physically impossible to get the work table square to the disk. Unbelievable. In the end I did some hard-core filing down of various key components and just got there.

Having got everything set up, one problem is that the sanding disk is of course mounted on velcro and so grinding a precise amount off is hard.

i.e. If you move a part onto it to a fixed, pre-set position, it seems to carry on grinding for an eternity but taking less and less and less metal off.

[The green arrow shows the small amount of the original face that I am deliberately leaving.]

Of course if you want to speed things up you can just move the part more deeply into the path of the sandpaper, and limit the depth of the cut by the TIME you leave it there.

Yes, this approach does broadly work, although the sand paper starts slightly bending around the part, and the cut face is no longer very flat!

But it's good enough to take the parts to my diamond whetstone to finish off.

Anyhow, thank you @JasonB for the inventive configuration.

PROBLEM SOLVED


P.S. The build quality of the Proxxon was pretty poor too. Did I mention that one of the 4 little screws to hold down the milling table simply could not be screwed in AT ALL. Luckily I found a spare old bolt with a thread that matches... but honestly!

Try the same setup but on the belt, it will cut faster and you won't have the velcro issue, that's what I used when I did my example.

And why I suggested a belt. If you get the direction of travel wrong you might still get some rounding - you want the belt travelling:

\
\
-> this way - off the thin end

Dave

What was putting me off using using the belt is that there is always a slight 'thump' where the sandpaper has been joined.  But, yes... good thinking, now that the slight curse of velcro has emerged.

I have now ground all the parts that I currently need, but I shall try using the belt next time.

I just discovered that instructions require a belt that is 100 x 914mm, rather than 100x915mm!

The problem is that I can't get the belt to lie very flat...

And I can't find any way to tighten the belt... other than using the belt tightening lever which has a fixed action.

Do you think that there is a meaningful difference the size that manufacturers make their sanding belts between "914 mm" and "915 mm" ?

J

Edited By John Smith 47 on 20/09/2021 15:01:54

Do you think that there is a meaningful difference the size that manufacturers make their sanding belts between "914 mm" and "915 mm" ?

J

No

Tony

Usual advice from the makers of diamond "whetstones" and wheels is to use them only for hard materials (carbide or ceramic etc) and not steels which are mostly "soft" in this context, and to use only very light pressure. Diamond is very hard but rather brittle, too much pressure will either fracture the diamonds or tear them from the wheel, and as has been said soft materials will clog the surface.

Rod

My SHARPAL Diamond Whetstone is specifically designed for use with knives which one tends to find are made out of steel.

I can see no mention of "a very light pressure". In fact I have heard people claim that a light pressure is bad for a diamond whetstone and that they prefer to be worked hard.

Water and a nylon scrubbing brush are suggested for removing of any metal particles that get stuck onto the diamond stone.

J

Fwiw, I have managed to get a bit more tension into the belt by jamming something (a nut & bolt) under the spring.

==> The ("915mm" belt now lies much flatter.

I shall report back after I next to some proper work using it.

J