Author Topic: Titivating A CNC Plasma Table  (Read 20516 times)

Offline awemawson

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Re: Titivating A CNC Plasma Table
« Reply #175 on: March 30, 2017, 02:31:16 PM »
So what about putting the bearing back together  :scratch:

Well in the end it took over two hours of frustrating eye strain  :bang: Several times I was nearly there - down to the last ten or so balls - when something slipped and I'd have to start all over again.

On each side of the slider there are two bearing sized holes parallel to the rail that at their ends point at the tangent point on the rail where bearings are trapped between the rail and the slider. If initially the slider is held in the correct alignment, balls can be pushed down these tubes from one end, and they will emerge between the body of the slider and the rail where the bearing action is happening.

However if the slider is ever so slightly off alignment the balls escape and get jammed in the wrong places  :bang:

Eventually I carefully measured the slider that was still intact, and put a small packing piece between the top of the rail and the under side of the loose slider to keep it in vertical alignment, with a tight rubber band around it to keep it together. Then it was a case of getting a few balls between the the rail and slider at the four tangent points to get the side to side alignment. Then 'just' a case of pushing bearings down the holes one by one until the holes and tangent points are full. Then quickly get the end cap on before it falls apart.

I probably repeated that process ten times  :bang: In one way the fact that the balls were magnetic was a help in picking them up with a tiny jewellers screw driver. But it was also a disadvantage, as, as you approach 'full tubes' several balls would decide to leap out and stick to the driver  :bang: :bang:

If I had to do it again, not only would I pack the vertical distance, but I'd make up something to go round the rails to fix the side to side spacing, that could be gradually withdrawn as the tubes filled and the balls emerged at the tangent points.

Anyway eventually it worked, and my headache hopefully will subside over the next few hours  :lol:

Andrew Mawson
East Sussex

Offline Spurry

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Re: Titivating A CNC Plasma Table
« Reply #176 on: March 30, 2017, 06:02:03 PM »
You must have the patience of a saint, Andrew. You did well not to lose any of the bearings too.  :clap:
From your experiences with these, would it help if the two rails were bolted to a piece of metal to keep the two bar ends in perfect alignment?
Neat result anyway, with those dinky little rails.
Pete

Offline awemawson

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Re: Titivating A CNC Plasma Table
« Reply #177 on: March 31, 2017, 03:00:27 AM »
Thanks Pete. Yes I think that you are right about bolting the rails together temporarily..the second bearing slider transferred ok but it was a  'heart in mouth' moment.

In fact I did lose two ball bearings. The way these work with the balls trapped in a straight line I don't think that it will make any difference, certainly there is no perceivable play or roughness, and comparing with the other one they feel identical.

I will have to transfer two more bearing sliders of the bigger THK 15 size soon, as I won a pair on eBay last night fulfilling my wish to have the main Z slide on four rather than two. All those holes in the recently made plate will now come into their own.  :ddb:
Andrew Mawson
East Sussex

Offline awemawson

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Re: Titivating A CNC Plasma Table
« Reply #178 on: April 01, 2017, 10:31:50 AM »
Got a bit of time yesterday and this morning to draw up and machine the prototype Floating Z slide. NB this slide will be limited to only about 10 mm travel by stops yet to be incorporated - it just needs enough travel to operate a micro-switch that detects the surface of the metal being cut by the tip of the torch touching and displacing the slide.

Again I incorporated three positions that the bearing sliders can occupy, as just with the full travel' Z slide, I'd like to source two more sliders to give more mechanical rigidity.

Next job is to hack these plates about to fit the limit switches, mounting for the cable guide and plugs and sockets. When that's done I'll incorporate the changes in the Autocad drawings and make the final versions. I also want to take a bit of weight out of them to reduce inertia.
Andrew Mawson
East Sussex

Online mattinker

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Re: Titivating A CNC Plasma Table
« Reply #179 on: April 01, 2017, 11:09:14 AM »
I can see that your going to entirely rebuild the plasma table to your usual exacting standards!

Glad to see you having fun! Matthew

Offline RodW

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Re: Titivating A CNC Plasma Table
« Reply #180 on: April 01, 2017, 11:10:01 AM »
Looking good.

Personally, I think adding extra blocks is overkill. a pair of them is rated to handle 457 Newtons of force. Divide by 9.81 and you end up with them being able to handle a 46kg weight at the end of  a 1 metre long lever! Your torch will weigh in at around 0.8 to 1.0 kg at a guess. Specs are here
http://docs-asia.electrocomponents.com/webdocs/0f44/0900766b80f448f1.pdf

Once I looked at the ability of my Hiwin HGR15 slides to handle such forces, I just went with one slide for the Z axis mount and the float switch.
RodW
Brisbane, Australia

Offline awemawson

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Re: Titivating A CNC Plasma Table
« Reply #181 on: April 01, 2017, 11:22:52 AM »
Thanks Matthew and Rod.

Rod, I've no doubt that they'll take the loading, but the existing Z main slide and floating Z slide are both based on single  HGR15 sliders, but there is noticeable wobble at the torch from the magnified microscopic play in the bearings due to the distance from the bearing to the torch. (About 145 mm of beam length)

So by sitting both sliding platforms on (hopefully eventually) four bearing sliders set a reasonable distance apart there is a good amount of triangulation so even a small amount of play will be constrained. It just seems a better engineering solution - due to the slightly heavier construction my beam length is increased to 157 mm (*) but the whole thing is far more rigid  :scratch:


(* actually that measurement is from the Z axis mounting plane so the actual beam length is about 60 mm less)
« Last Edit: April 01, 2017, 01:25:30 PM by awemawson »
Andrew Mawson
East Sussex