4th axis tombstone material choice

owenhooker · Jun 25, 2017

I'm in the process of designing a 4" square x 18" long tombstone for my hrt160. I am hoping to get some feedback from others as to wether I should use steel or cast iron? Would class 40 gray cast iron be a good fit or should i go with the higher strength of something like 4140? I do like the idea of having better dampening with the cast iron but i'm wondering if it's better to have the strength from the steel instead.

Larry Dickman · Jun 25, 2017

I made mine from 1018. No reason to go with anything more exotic.

gbent · Jun 25, 2017

Whatever is easy to find in a convenient size. As Larry said, 1018 is fine. The deflection of all steels is the same, and the deflection will make bad parts long before the strength becomes an issue. I've made them from heavy wall square tubing before.

owenhooker · Jun 26, 2017

So I gather you don't think it's worth using cast iron for it's dampening properties? did you have any issues with the 1018 warping when machining the tombstone square?

Shawnrs · Jun 26, 2017

I would ask what kind of parts are you intending to put on your tombstone? We use aluminum cast tombstones and mounts steel sub-plates to them. The cast iron tombstones we had were too heavy and put restrictions on our machine.

Larry Dickman · Jun 26, 2017

owenhooker said:
So I gather you don't think it's worth using cast iron for it's dampening properties? did you have any issues with the 1018 warping when machining the tombstone square?

Cast iron would be ideal, but for 1 piece, impractical. I tried to find some heavy wall square tube but struck out there. I used 1" thick cold rolled, all bolted and doweled. Once assembled I finish milled the four sides on center. No warpage of any kind.

owenhooker · Jun 26, 2017

At the moment all the parts i'm making are aluminum but I want to build it thinking that I may cut harder materials on it in the future. My plan is to bolt on aluminum fixture plates. I figure the tombstone would weigh about 100lb if made from cast iron.

I haven't checked with my metals supplier yet but just looking at speedy metals class 40 grey cast iron prices it doesn't look like it would be any more expensive than using 1018.

metlcutr55 · Jun 28, 2017

shop I just retired from had many built from aluminum tooling plate, initially bolted, then welded, then surfaced in place. I was aghast seeing this. but an excellent programmer and engineer of many years there assured me these had never caused a problem, working tolerances in the .001 range. still sounds wrong to me, but we made the parts to tolerance day in and out.

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4th axis tombstone material choice

owenhooker

Plastic

Larry Dickman

Titanium

gbent

Diamond

owenhooker

Plastic

Shawnrs

Stainless

Larry Dickman

Titanium

owenhooker

Plastic

metlcutr55

Cast Iron

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