I make leather cutting dies, how to lose less time to prepare the raw material ?

Hello everyone,

it's been almost one year since I started out to mill steel on my Tormach PCNC1100, I still have alot to learn but there is one thing I must improve ASAP, because I loose a lot of time in the first stage of the process, when I have to prepare the raw material to mount it in the vise.

I get my materials from 2 different suppliers.

1. The main supplier also sells small parts of 1.2379 steel, like 50x50mm, from time to time I go there and get small block to make more cutting dies, I search for blocks that fit almost perfectly the final product size, so I will need to mill as less as possible.

Those blocks are cut from larger blocks, and usually all sides have marks from their huge bandsaws, I had success in facing those on the mill using Tormach 38mm facemill, but still slow as the blocks are not parallel, sometimes I have to add a round broken drill between the vise jaw and the steel block, because otherwise the vise will only hold in left or right side of the block. Using something round in the middle, was ok , I just used this method twice untill now, with success.

Attachment 374386

2. The second supplier sells longer (1 meter ) FORGED steel bars, this was a good choice for me as I quite often I need to do even smaller parts, like 10 x 20mm (15mm thick) and this small size blocks can't be purchased from the main supplier, also he can't cut slices so small on their big bandsaws.

The main problem with this material is that is uneven and when I try to facemill with the Tormach 38mm facemill, the carbide inserts get dull (tear very easily or get chipped). I think the surface of the forged bars is very hard compared to the inner section, which is milling ok. I tried to mount new carbide inserts twice and each time the inserts got dull in less than a minute.

Maybe one reason is the cutting depth I used, it was quite small: 0.3mm. Is this to small for the carbide inserts ? When the block is large enough I use 0.5mm or 1mm (this was the maximum depth of cut I used)

This is a forged steel bar:
Attachment 374388

For the last cutting die I made from the forged steel, I spent some time (maybe ~ 15minutes) to sand all the faces on the belt grinder, until there was almost no black spot on the face of the material, but still after this I had more work to do on the mill, to make the side parallel, sometimes I spend ~1 hour only to prepare the material, to make it parralel and have all sides faced flat :(

I started to look over a surface grinder, I don't want to spend $4k for a Tormach grinder, the size is enough for me, and I like as it does the job almost automatically, I know there are alot of machines on ebay, but I'm not sure if this will help me out to "square" a block faster. Also some of my blocks are wide, and I will need to make the sides parallel one to another, the magnetic table will hold the block when mounted on the tall side ? or I need to use a vise to mount it like that?

Quote:

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Originally Posted by Steve Seebold

Before you grind a block like that, I would have machined it close to size (within .010 of finish size) then go to the grinder to finish it.

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I read some threads and seen a message from @Steve Seebold, is it recommanded to grind the uneven metal first on the surface grinder and only than start to mill it ?

Any advices are welcome, for facing faster the forged blocks, or any method to make easier a block of steel parallel so it can be safely mounted in the vise.

Bellow are a few photos with a cutting die I finished last night

Attachment 374390

Attachment 374392

If this stuff is dulling your carbide cutters, it's probably too hard to machine. Try annealing it first, machining it to the near-net shape, then hardening and tempering it, saving the grinding for when that's all done.

@awerby I only have issues in the first stage, where I need to flatten and make all side parallel, and only the small carbide inserts get dull, with the cylindrical 4 flute carbide end mills I can mill the surface, but slower as the largest end mill I have is 12mm. The facemill is 38mm in diameter, it's much quicker in facing all the sides.

This is why I was thinking if I can grind first on a surface grinder, to make all the side parallel on the grinder, and only than to mount the part in the mill. Can I use a surface grinder to make clear off the surface of the forged material, if the sides are not perfectly flat, can I use the magnetic table ? If not, should I use a vise on the grinder too ?

The hardness of the material is around ~220HB (but I don't know if the black uneven surface of the material has the same hardness or a higher one )

It might be dulling the inserts because you're trying to spin the facemill too fast. But sure, if you have a surface grinder, I don't see how it would hurt to use it as a first step. If you need the top and bottom of the plates to be perfectly parallel, then you should grind both sides. If the first side is so rough that the magnetic chuck won't hold it while that happens, then yes - you'll need a vise or something to hold onto them.

What you are trying to cut through is called ''mill scale'' it's nasty stuff to try to get through. You would be best to cut as deep as you can on the first pass to get to the base metal. 0.75 mm should be enough to get through it. Maybe slowing down the spindle speed would be a good idea. If I were doing that with a 38mm cutter, I would be turning about 400-600 RPM for the roughing pass, C5 inserts would be prefered.

A surface grinder is not the right tool to try to remove mill scale. The wheel will instantly gum up and really won't cut. I have tried this. The best grinder for removing mill scale is an angle grinder with a coarse wheel, but even that does not work well.

Just soak the steel in Hydrochloric acid / water mix for 1/2 hour or so, scale will all be gone.

@Jim Dawson Thanks for the intormation, the last cutting dies I made I tried to first use the belt grinder on the sides where there was mill scale, and than only mill the side on the mill.

Quote:

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Originally Posted by Gippy

Just soak the steel in Hydrochloric acid / water mix for 1/2 hour or so, scale will all be gone.

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I will give it a try to see what is happening :)

I'm now in the process of finding a good metal band saw, with a 0.9mm thick band and at least 20mm tall, my current band saw is to small and it takes forever to cut a 20x40mm tool steel in half. Maybe if I will have a better bandsaw I could use this also to cut mill scale, if the material is thick enough.

Sometimes I need to mill maybe more than 10mm on the exterior of the part, because the raw material is bigger than the final part, what do you guys usually do? cut the material as close as you could on a band saw and than start milling, or mill it using the mill all around, even if you need to mill 10mm of material all around (on 30mm thick part)

Unless you need to make curved cuts, I'd suggest using an abrasive cut-off saw on that tool steel. Replacing bandsaw blades gets expensive after a while.

Doesn't the abrasive discs change the properties of the material (maybe hardening ?) when cuting the material ? I don't know why I never seen anyone cutting using abrasive discs (I didn't see to many workshops, or steel suppliers)

I don't know why, but on every shops or suppliers iI've been to , they all use band saws to cut steel, bandsaws and flood coolant.

Squaring up a block is time consuming, but no way around it. I rough out most tool steels with a bandsaw, normally no coolant. I like bimetal blades for that work.

Bimetal blades definitely recently had to opt for a standard will go back never again.:D

I think I will get a CORMAK BS 170G , this has a much larger blade than my current bandsaw (13x0.6mm compared to 20x0.9mm on the Cormak) I hope this new tool will make my life easier :D Will let you guys know what I ended buying and if it does the job as I expected.

Bellow is a photo with a few pieces of tool steel (1.2379) that I usually need to cut using the bandsaw.