Steel or Aluminum,that is my Question

I was planning to build my CNC router from welded 100mm x 100mm x 6mm SHS steel utilizing a high side wall design so I could get the top rail mounting surfaces machined co plainer and also keeping the gantry pillars short.
I accepted the fact that the machining of the rail mounting surfaces was going to cost a small fortune, about $600 Australian.

Now I have to decide if the welded frame first needs to be stress relieved at about $850 plus about $1000 in freight.

Would that budget be better spent constructing the CNC out of heavy 160 x80 aluminum extrusion?

Have you thought about using slow epoxy with a moat to achieve the above?

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Originally Posted by Clive S

Have you thought about using slow epoxy with a moat to achieve the above?

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I did think about that but wasn't sure if it would be accurate enough
I still have the issue of whether to get the frame stress relieved or not.
.

G'Day Spud
What post code are you?
That's a lot of freight?
How big is it?

Have you considered bolting the steel together?
No stress relieving needed.

Can you use CAD?

If so draw up some 5mm steel plate brackets for stiffening all the joints put in all the holes as well to form strong corners. And get them laser cut. For 5mm steel the minimum hole size is 5mm.

My guess is a couple of hundred maybe 3 hundred would pay for a lot of brackets inc the steel. Once you are happy with the design glue all the joints together with metal filled epoxy and bolt them up for keeps.

I live in Melbourne OZ

Regards
John

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Originally Posted by spudym

I did think about that but wasn't sure if it would be accurate enough
I still have the issue of whether to get the frame stress relieved or not.
.

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Well a lot will be what you want to achieve with the machine ie what tolerances you need and what you what materials you want to machine.

Its always a good idea to draw the machine in cad first.

Steel, absolutely.

You can heat-treat it yourself .. a ghetto solution works fine.
Put up a fire, chuck it in, after 30 mins in coals, cover with sand, take out next day, done.

Even nasa did the big Apollo 11 parts like this, back in the day.

You can easily sand to about 0.02 mm accuracy, using a large wide belt sander.
You really want the best most powerful sander you can loan or rent for a day, about 40 grit belts.

Mark out where you want the material to come off, by using a sharpie crosswise.
Where the marks have come off you went about 0.03 - 0.04 mm deep.

It is very fast, but noisy and unpleasant.
I did 2.2 m long ways like this, in 20x50x2200 mm tool steel flats, and 30x80x100, welded / bolted to substrates.

A ground straight edge of some type is necessary, strong light behind, you can easily see 0.01 mm errors.
My vertex 1000 mm straightedge (woodworking, surprisingly) is good enough, guaranteed to 0.04 mm over 1 m. About 100€ ebay.
The machinist ground straightedge is more accurate, but only 40 cm long.

It takes only about half an hour to do one surface to about 0.01 - 0.02 mm.
Edges do get rounded, so only the center is pretty flat.

I use a Festool 105 sander, best in the world, 1200W, but it is very very expensive. (Noisy). Use earmuffs.
Just rent the biggest possible wide flat belt sander, maybe 30$ for one day.

If the beams are bent, they are easily straightened with some 24 mm all-thread and 80x80 tool steel flats drilled through, used as a press.
I did no heat treating, simply sanded straight, since the tool steel flats are almost straight already.

Look at how metal boats are welded, online.
Tacks, widely spaced, opposite corners, bit at a time. Do not weld all-in from one end at first - this will bend it.

Hi Clive,
I want to be able to machine MDF and hardwoods mainly but also do a bit of aluminum.
I am struggling to learn Fusion360 at the moment.

Matt

Hi John,
I,m from Cowra NSW 2794 and the heat treating facility is in Brisban.

I was thinking about bolting it but figured you would still need to weld brackets and lugs on anyway which would cause stress.

I use Autocad and I am trying to learn Fusion 360.

Could you elaborate on using epoxy? is that so the plates bolted together just can't slide.

Matt

We actually have a huge bonfire ready to burn in the back yard as soon as the weather cools down,
I would much rather put the money into better ball screws and running gear then pay to ship the frame all over the country side.

Hi Spud

The link below is a PowerPoint presentation a while back, It details how I made an epoxy bearing material using epoxy, metal powder and some low friction materials. Teflon, molybdenum disulfide, and graphite, these three elements are not needed for an epoxy grout. You can make a thick paste from epoxy and iron powder alone that will make an excellent high strength grout for filling the small voids left between machine members.
As you live in Australia the sources at the end of the PowerPoint are relevant.

http://www.mediafire.com/file/022r26...mpact.ppt/file

The link below is to a great build done some time ago. The post clearly explains how the builder used epoxy to grout joints before bolting.

http://oneoceankayaks.com/madvac/madvac_index.htm

Hope this helps

Regards
John

Quote:

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Originally Posted by spudym

Hi Clive,
I want to be able to machine MDF and hardwoods mainly but also do a bit of aluminum.
I am struggling to learn Fusion360 at the moment.

Matt

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I used epoxy like others have done. http://www.mycncuk.com/threads/6403-...ts+epoxy+clive post #6

Re;- I want to be able to machine MDF and hardwoods mainly but also do a bit of aluminum

Wood will shrink and ali will change with the temperature so I think 0.05mm is fine for accuracy .