Author Topic: Titivating A CNC Plasma Table  (Read 9720 times)

Offline awemawson

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Re: Titivating A CNC Plasma Table
« Reply #150 on: March 19, 2017, 03:57:50 PM »
Since I first got this machine I've not been overly happy with the Z Axis. It's main mounting plate had been bent at one time, and both the normal Z movement and also the 'floating Z Axis' used for material sensing only ran on single  linear rails, resulting in a bit of side to side wobble and tilt. Don't get me wrong - it works - but it's not overly robust in it's design and there were features that I wanted to incorporate - namely:

A/ Dual parallel rails for the main Z and the floating Z movements

B/ A Magnetic Breakaway Torch Mount

C/ Emergency Stop to be asserted if the Magnetic Breakaway is triggered

Now this is all very well, but I didn't want to strip down the existing Z axis and hence stop me using the machine, while building the new one. So I decided to start from scratch and make a modular Z axis that would be on plugs and sockets and fit existing mounts on the machine.

I procrastinated for a long time, looking at economical ways of getting the linear ways, ball screw and nut, bearings etc until eventually a 'Prototype Z Axis' turned up on eBay. It had been put together but obviously never used, and would need re-making, but it had the linear rails, ball screw and nut, bearings, stepper etc just as I wanted, but for far less than the total of buying the separate items  :clap:

« Last Edit: March 19, 2017, 04:35:58 PM by awemawson »
Andrew Mawson
East Sussex

Offline awemawson

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Re: Titivating A CNC Plasma Table
« Reply #151 on: March 19, 2017, 04:05:57 PM »
The end mounting plates will need re-making to spread the rails further to suite the existing machine mounts, the coupling between the stepper motor and ball screw was rigid, and I'll have to mount a new floating Z axis on it with suitable magnetic breakaway torch holder and limit switches.

So - buy an Oldham coupling and bore it to the correct sizes - simple (and done  :ddb:)

Draw up a CAD drawing to show how all the components potentially interfere with each other, to make sure that the new upper and lower plates will work - done  :ddb:

Buy a handful of limit switches - done  :ddb:

Andrew Mawson
East Sussex

Offline awemawson

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Re: Titivating A CNC Plasma Table
« Reply #152 on: March 19, 2017, 04:12:00 PM »
Buy a big slab of 10 mm thick aluminium alloy ground tooling plate to make the bits - done  :ddb:

Source a (VASTLY EXPENSIVE  :bugeye: ) Magnetic Breakaway Torch Holder - done and customs duties paid  :ddb:

(I had intended to make my own, and even drew it out in CAD and bought the magnets, then I realised that the 'real ones' had been carefully developed to hold on in normal situations, and let got if the torch catches the plate and the amount of magnetic force needed was a great imponderable, and with torches about 600 each I didn't want to carry out tests !)
Andrew Mawson
East Sussex

Offline awemawson

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Re: Titivating A CNC Plasma Table
« Reply #153 on: March 19, 2017, 04:21:35 PM »
Source some smaller THK-10RM rails and sliders for the floating Z - done but will need cutting in half  :ddb:

So now it is a case of making the end plates - (simple but need doing accurately) so I extracted them as individual parts from the CAD montages and will probably CNC machine them.

Still quite a few details to work out re the floating Z and limit switch mounting, but I'll get the end plates made so I have something to prod and poke !
Andrew Mawson
East Sussex

Offline awemawson

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Re: Titivating A CNC Plasma Table
« Reply #154 on: March 19, 2017, 04:23:18 PM »
Incidentally, the pre-existing mounting slots that I previously referred to are these:

Andrew Mawson
East Sussex

Offline philf

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Re: Titivating A CNC Plasma Table
« Reply #155 on: March 19, 2017, 05:46:36 PM »

So - buy an Oldham coupling and bore it to the correct sizes - simple (and done).


Andrew,

I'm not usually a pedant but that coupling is a Lovejoy type coupling and not an Oldham!

An Oldham coupling wouldn't work in that application because they have no lateral stiffness and would need a bearing to support the screw.

http://www.oepcouplings.com/assets/ocanimationsmall.gif

The Lovejoy type couplings allow angular misalignment only and no (or very little) axial misalignment.

Cheers.

Phil.
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Location: Marple, Cheshire

Offline awemawson

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Re: Titivating A CNC Plasma Table
« Reply #156 on: March 19, 2017, 05:53:06 PM »
I bow to your knowledge Phil  :bow:


The vendor referred to it as a Plum coupling  :scratch:
Andrew Mawson
East Sussex

Offline awemawson

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Re: Titivating A CNC Plasma Table
« Reply #157 on: March 20, 2017, 06:19:06 AM »
Well the upper and lower plates are 'VIRTUALLY' done but no time yet for the real things, also need to resolve the usual fixturing issues  :scratch:

(I marginally altered these from the CAD drawing above, reducing them to 145 x 68 to take a bit of weight out of the assembly and also give a bigger  'waste' for the milling, as the source plate is only rough sawn at a nominal 150 mm wide.)
Andrew Mawson
East Sussex

Offline awemawson

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Re: Titivating A CNC Plasma Table
« Reply #158 on: March 21, 2017, 11:58:42 AM »
I got time today to finish the upper and lower plates for the Z axis.

Each was a two stage process - boring and drilling the holes, then making a profiling fixture and profiling their periphery giving the corners a 3 mm radius.
Andrew Mawson
East Sussex

Offline awemawson

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Re: Titivating A CNC Plasma Table
« Reply #159 on: March 21, 2017, 12:00:24 PM »
This has allowed me to get to 'first trial assembly' so that I can better decide what layout to use for the travelling stage that mounts the 'floating Z axis' and the actual torch holder
Andrew Mawson
East Sussex

Offline awemawson

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Re: Titivating A CNC Plasma Table
« Reply #160 on: Today at 10:16:29 AM »
A bit tied up this morning collecting and distributing 'self assembly lamb kits' (ready for the freezer) but I did manage to do a bit of drawing up the 'front plate' that will hold the 'floating Z axis slider'.

This is a bit of reserved design, in that I am undecided on exactly how I will locate both the HSR-15 sliders and the ball nut location, so each have three alternative positions - being CAD then CAM it's as easy to let the machine do all three alternatives and I can pick and match as it evolves - then if I'm REALLY keen I'll make another with just the selected holes in it.

Meanwhile the plate will look like a bit of Emmental cheese  :lol:
« Last Edit: Today at 02:58:15 PM by awemawson »
Andrew Mawson
East Sussex

Offline AdeV

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Re: Titivating A CNC Plasma Table
« Reply #161 on: Today at 11:44:39 AM »
What you need is a lump of plastic-like material which can be machined very quickly and easily in order to prototype the finished article. You know, something that doesn't cost a fortune, and doesn't break cutters if you get a tool-crash, and who's chips can be melted down and reformed into new blocks.... 

:lol:
Cheers!
Ade.
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Offline awemawson

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Re: Titivating A CNC Plasma Table
« Reply #162 on: Today at 03:00:42 PM »
 :lol: :lol: :lol:

Got a cupboard full of machinable wax Ade  :ddb:

Not really applicable here though - it would break  :(
Andrew Mawson
East Sussex

Offline AdeV

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Re: Titivating A CNC Plasma Table
« Reply #163 on: Today at 04:43:46 PM »
Got a cupboard full of machinable wax Ade  :ddb:

You might very well think that, I couldn't possibly comment!  :palm:

Actually, you'd be surprised how thin you can go and have it hold together; but yes, one overtightened bolt and before you know it you've got a pile of bits all over the floor....
Cheers!
Ade.
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Or: Zhengzhou, China. An even longer way from anywhere...
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Offline awemawson

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Re: Titivating A CNC Plasma Table
« Reply #164 on: Today at 04:55:08 PM »
... No I really DO have a cupboard full of the stuff Ade, but now we know that you do as well   :clap:
Andrew Mawson
East Sussex