Milling flat surfaces Harden tool steel

[Cp5010]

HI, Folks

Need an expert advice on milling harden tool steels (60-62 Hrc) mostly flat surfaces.. Currently using End mills but Its not efficient and  not holding flatness and tolerances (+/-0.0002). Need advice on specific tools and strategy for machining it. 

Thanks. 

[Jobnt]

I don't think you'll hold .0002 with machining process, I think you'll have to grind it.

That being said, depending on how big the part is you might have better luck with a face / shell mill with carbide or even ceramic inserts and then surface grinding to the .0002 spec.

[Cp5010]

@Jobnt Parts are not that big, 10 x 10 inches max. Parts have 3d features on it raised pads and V-rings Etc., so grinding is not appropriate for the application. 

[Jobnt]

Two tenths (±0.0001) flatness is a big ask for a machining process. 

If you can post an example of the shapes in question and where the tolerances apply we might be able to come up with a solution. 

[#Rekd™]

What material is it? Like @Jobnt said this is a tall task for a part of that size!!!!!!

What machine and what kind of holders are you using?

What end mill brand are you using?

Union Tool makes specific tools for machining hardened materials. 

[Cp5010]

@Rekd Materials are mostly S390,M4 and D2. Machine is Makino Ps95 and mostly hydraulic holders. Endmills are from Deboer tools. 

[#Rekd™]

IMHO you will never hit that tolerance with hardened D2 over that large of an area.

Deboer isn't listing any end mills for hardened steels that I can see.

[Leon82]

You will not hold that on a PS95 all the pads will be a different height. Hopefully yours is newer and more improved than ours.

[BSmith23]

How thin is the area that you are trying to keep flat?  And how are you holding the part to the table?  We use YG-1 end mills on 60+HrC D2 and have pretty good results with them.

[rgrin]

Would a CBN cutter do any better? I have only seen them used and haven't had the need to try them yet. I saw Adam the Machinist on Youtube have good success with them, but he was side cutting. IDK how they handle facing toolpaths

[sweeden5050]

I would use a face mill which can cover the surface in question( if possible) I would leave the dimension heavy .001-.002 for grind. 

[jpatry]

On 7/26/2023 at 9:28 AM, Jobnt said:

I don't think you'll hold .0002 with machining process, I think you'll have to grind it.

Was gonna say something else, but then I did a double take and saw the .0002 tolerance.

This reminds me of when the company I work for quoted a job without looking at the fine print and seeing that the drawing incorporated by reference the customer's internal standard which stated that all such parts and resultant assemblies had to be machined and assembled in a cleanroom, three different and excruciatingly detailed cleaning processes, and finally put through an autoclave.

[crazy^millman]

3 hours ago, jpatry said:

Was gonna say something else, but then I did a double take and saw the .0002 tolerance.

This reminds me of when the company I work for quoted a job without looking at the fine print and seeing that the drawing incorporated by reference the customer's internal standard which stated that all such parts and resultant assemblies had to be machined and assembled in a cleanroom, three different and excruciatingly detailed cleaning processes, and finally put through an autoclave.

30 years ago the owner of the shop I worked in quoted a job for 30 foot long machine parts for a robot company. They wanted .001 flatness and parallelism with .0005 true position on 1000 holes with +/-.0001 on diameters across the 6061 Aluminum extrusions. Our longest machine was 60 inches. They were going to farm it out to a shop that had at the time a 50 year old manual machine. I laughed when I saw 20 hours to machine that part. They mistook 30 feet for 30 inches and .0005 true position for .005. and flatness for .01 and .001 on the hole sizes. They wanted 20 of these parts and they thought they were going to make a killing when they got the PO for 400 hours. I think after 6 months and never making the first part good they finally gave the job back to the customer. The funny thing was the end customer didn't have a CMM and hen i asked them how they going to check them they said well per the PO your company has to provide a full NIST traceable CMM report. I was of few people in North Florida at the time who even knew what NIST was. Jose came from Moore Tool who use to be the shop foreman there to work in our shop. I learned so much about machining tight tolerance parts from him. He said each part was $1,000,000 if he even attempted it, but didn't know of any equipment at the time in the world that could do it. He said that was their normal get lost quote to anyone who came with stupid stuff like that. I adopted that for jobs I did want to take over the years.

[jpatry]

7 hours ago, crazy^millman said:

i asked them how they going to check them they said well per the PO your company has to provide a full NIST traceable CMM report.

Truly magical