Thread: Newcastle: Large mill / planer / grinder needed for job

Thanks for all the input and suggestions everyone. Sorry for slow reply.

A taut wire had not occurred to me. I'll look in to that as a method.

Originally Posted by PDW

There are plenty of epoxies available. Devcon liquid steel comes to mind but no idea on price. I use quite a bit of epoxy for woodwork, I buy it from the boat shops. There's a nice non-slumping type used for fillets etc.

All depends on the applied load.

Yes, for the same flange width. However a 150mm parallel flange channel is going to be a lot stiffer than 100 x 100 x 3 RHS. You want depth for stiffness more than width so using square section is a mistake anyway.

I'll do a bit more research on what epoxies are available.

Originally Posted by PDW

This depends entirely on your mill; a horizontal mill is excellent for this sort of work. The mill that Evan has, no real problem. My old Victoria U2 can do 700mm length of cut so 3 moves as follows:

Bolt alignment guide to table. Couple of angle plates for example.

Cut.

Shift 2/3 and use DTI on machined section to keep parallelism.

Cut.

Shift etc.

Scrape off ridge where interrupted cuts start & stop.

It'll come out well within your stated tolerance *provided* the material doesn't stress-relieve which IMO is another good reason for using parallel flange channel. It's hot rolled and has a lot less locked in stresses than RHS.

That's exactly how I had thought to do it, but the difficulty I see is that tube or parallel flange or universal beam will all be uneven to a reasonable extent on multiple surfaces. This means when I move the beam along it may end up slightly tilted (e.g. not square in the vertical plane) even if it is square in the horizontal plane. It's possible obviously (otherwise large accurate machines would not exist) but could be very painful.

Originally Posted by PDW

As I've said I think using square RHS is a big mistake. If you want stiffness, 150 x 75 RHS is going to give it to you a lot more than 100 x 100 is. Somewhere there's a deflection table for this stuff but I can't remember where - that's what you want to know, not what someone else on the net has done.

I've looked at deflection tables and calculators (plenty available on google, though it can be hard to find metric ones). The load will not just be vertical on the beam. There will also be horizontal and torsional loads from the router cutting which need designing for also. I'm aware of the effect that increasing the section has on stiffness / deflection. Doubling from 100x100 to 200x200 results in 10 times the moment of inertia. I'd been looking at a 200x200 beam for my gantry.
Example sites:
structural steel & oil field suppliers,channels, sections, angles, sheets, bars & gratings, beams, flange beams, columns,
Steelweb Steel Section Data - Structural

Lets compare a universal beam of about the same weight (therefore cost) (100 uc 15 Steel Data) to 100x100x5mm square section (100 x 100 x 5 Steel Data)

Universal Column

Weight: Overall Overall Flange Thickness: Web Thickness: Root Radius: Moment of Inertia - XX Moment of Inertia - YY

14.8 kg/m 99.0 mm 97.0 mm 7.0 mm 5.0 mm 10.0 mm 3.18 million mm**4 1.14 million mm**4

Square Hollow Section

Weight: Overall Overall Flange Thickness: Moment of Inertia - XX Moment of Inertia - YY

14.2 kg/m 100.0 mm 100.0 mm 5.0 mm 2.66 million mm**4 2.66 million mm**4

The SHS is much stiffer in the Y direction whilst being slightly less stiff in the X direction. That's without looking at torsion, where the I beam falls down particularly.

At the end of the day we are talking wood and plastic cutting forces, which are no where near steel cutting forces. Stiffness does have very real advantages in accuracy etc.

Originally Posted by PDW

What you have to realise is, this is a hobby for you and businesses aren't going to be interested as you are obviously not prepared to pay. Yes, we do know of at least one place that can do it. Marco comes to mind. In Melbourne. The starting price is likely to be around $2500 with no guarantees because of the nature of the material.

Find someone with a 1500 to 1800 long precision straight edge (good luck there, too, I know where there are 2 of them. One in Melbourne and one in Hobart). Or use the taut wire and sag tables to do the same. Spot your RHS or channel after getting rid of any mill scale etc. Use a die grinder to knock down the high spots then shim or bed in epoxy. You probably only need a series of planar spots every 100mm or so, the rest could be slightly lower. That will teach you a lot as well as being faster, probably, than finding someone who will do the machining for you in return for the equivalent of a slab of beer etc.

Yep, exactly, this is a hobby. Thus my asking if other members, most of whom are hobbyists also, if they had a suitable machine.
I have not approached businesses, nor will I do so, as I'm well aware this would be overly expensive as a single job.

Originally Posted by pippin88

That's exactly how I had thought to do it, but the difficulty I see is that tube or parallel flange or universal beam will all be uneven to a reasonable extent on multiple surfaces. This means when I move the beam along it may end up slightly tilted (e.g. not square in the vertical plane) even if it is square in the horizontal plane. It's possible obviously (otherwise large accurate machines would not exist) but could be very painful.

However you approach it, it's going to be very painful. That's the nature of what you're trying to achieve. Especially if you want more than one side straight, flat *and* at 90 deg to the other(s).

I can think of a few ways to fixture on a HM to do it but if you don't have access to one, there's probably no point. Short form, machine one face until you run out of travel then set up an angle plate or parallel bolted to the table edge so you can clamp onto the machined vertical face then keep traversing along. You're always clamping on the vertical machined surface after the first cut and can check for wind. Reduces your available travel some but that's a tradeoff. Other clamps and distortion prevention due to clamping I leave as an exercise for the operator....

I've made some pretty long angle plates like this on a HM using a big face cutter in the spindle but never had to reset so I can't say with 100% confidence that you won't get some variation from a single plane - but then I'd give no guarantees the steel won't banana on you as soon as you cut it anyway. It's the nature of RHS/SHS to do that....

Good luck with it.

PDW