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dudz
02-12-2012, 01:46 PM
My table on my "3 axis cnc/router" is a vacuum table, but the x axis is a moving axis, so I would assume it is difficult to use a pump with lines across the rails. Where can I get a "bolt on" replacement bed the same size with pre-drilled clamp holes ? The bed measures 450x300mm. / Or would it be a better idea to buy a vacuum pump ? but these seem very expensive. I plan to mill alu, cut plastic and carbon fiber.

Jonathan
02-12-2012, 03:05 PM
If you need to mill alu then a vacuum bed is not much use since it's not going to hold aluminium. A combination of both would be good...

I could make you a bed with an array of tapped holes, or T-slots, from aluminium on my router. How thick would you want it? 20-25mm?

dudz
02-12-2012, 03:19 PM
25mm sounds good Jonathan. I guess I need to take the existing bed off, to measure where the mounting holes would be and the sizes etc...?

dudz
02-12-2012, 03:28 PM
I have alot of extra unused height above the Z axis rails, so I could move the spindle and Z axis up at least 50mm. I am just a little worried that when I undo the bolts and move it all up, I might not get it all "exact" to less than a mm for trueness and squareness . I have no gauges of any sort, and I wouldn't know which one I needed.

dudz
02-12-2012, 06:31 PM
Just measured the distances between each side of the Z axis rails etc... There seems to be a couple of mil out on several parallel measurements. So I guess I shouldn't worry about moving it all. I know I can get it better than this.

AdCNC
02-12-2012, 11:15 PM
Jonathan, how long did it take you to drill and tap all your holes on your bed? or is it an on going process?

Jonathan
04-12-2012, 12:55 AM
or is it an on going process?

Yes it is - I'm just tapping the holes as and when I need them.


25mm sounds good Jonathan. I guess I need to take the existing bed off, to measure where the mounting holes would be and the sizes etc...?

If you can provide a drawing showing the existing hole positions and the array of holes that would be ideal. I've just noticed though, from the thread where we were discussing buying the machine, that the machine already has a tapped aluminium bed so I'm not sure why you need another one?

dudz
04-12-2012, 07:41 PM
The existing bed has hundreds of vacuum holes, but only 4 tapped holes. The question is.....do I ruin a half decent vacuum bed by drilling and tapping it all out or make a new one ?. The vacuum bed is only 12mm thick, plus the plastic underneath which is 13mm thick.

Jonathan
04-12-2012, 09:05 PM
Fair enough...
The easy option is to just get the 25mm aluminium plate, mill it to size and drill the array of holes in it. Alternatively use the same thickness, but mill slots into it then add strips on top (something like 1.1/4"x3/8") so that you end up with T-slots which makes clamping much easier. In addition this means you can skim the bed flat a few times, or accidently make marks in it without worrying too much since the strips can simply be replaced which wont cost much.

dudz
04-12-2012, 09:34 PM
What sort of clamps are there for that sort of set up ? or do you make your own ?. I suppose 10mm T slots ?

I try to buy everything on ebay for ease. What grade of Alu should I get for the bed ?

Jonathan
04-12-2012, 10:01 PM
What sort of clamps are there for that sort of set up ?

http://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=m570.l2736&_nkw=milling+clamps

But you can use just about anything really...


or do you make your own ?. I suppose 10mm T slots ?
There are quite a few examples of homemade ones on forums. 10mm should be fine.



I try to buy everything on ebay for ease. What grade of Alu should I get for the bed ?

6082 is generally the best value. Aluminium is really expensive on eBay. www.aluminiumwarehouse.com (http://www.aluminiumwarehouse.com) will be much cheaper, or I use Metal Stockists: ASC Metals Lincoln Ltd. - Metal stockholders for East Midlands/North of England (http://www.ascmetals.com) as they're even cheaper...

dudz
05-12-2012, 05:54 PM
Seeing all my rails are 25mm round (unsupported) do I really need to replace them with supported rails ? I see that most machines of this size only have 16 or 20mm supported rails.

Jonathan
06-12-2012, 06:22 PM
Seeing all my rails are 25mm round (unsupported) do I really need to replace them with supported rails ?

Yes, if you are not satisfied with the current rigidity of the machine. Even 12mm supported is likely to be stronger than 25mm unsupported over a reasonable distance, but that doesn't meant you should use 12mm:
http://www.mycncuk.com/forums/faqs-problems-solutions/4356-why-not-use-unsupported-rails.html


I see that most machines of this size only have 16 or 20mm supported rails.

For much of history most people believed the earth was flat, but that didn't make it flat!

dudz
21-12-2012, 06:29 PM
Ok... I have the 25mm Aluminium for the bed. I unbolted the original vacuum bed, and noticed straight away that it is bent down on each end where there are no bearing blocks supporting it. 4mm to nothing, from each end to the center !
I took out the 25mm unsupported rails and rolled them on a sheet of glass to check for bend. Seems all ok. The vacuum bed is pretty flimsy. 2 out of the 4 bearing blocks seem to have had their day ( roll a bit rough ). So I suppose I might aswell replace the 25mm rails for supported ones with new open bearings ; SBR20X900 Precision Supported Rail kit 900mm long CNC | eBay (http://www.ebay.co.uk/itm/SBR20X900-Precision-Supported-Rail-kit-900mm-long-CNC-/121036052880?pt=UK_BOI_Industrial_Automation_Contr ol_ET&hash=item1c2e4f9990)

The rail length I need for the X axis is 850mm. Is 20mm rails (as in the link) going to suffice ?
Also the ballscrew seems fine. But as I am replacing the rails, will the height from the 45mm profile (frame) to the bottom of the new Bed be the same for the new rails and the original ball screw bearing ? The new rails are certainly within 2mm (see pdf on ebay link )

Jonathan
21-12-2012, 06:40 PM
If you're planning on getting the rails from that seller then you can get 25mm for the same price here (http://www.ebay.co.uk/itm/2-x25MM-FULLY-SUPPORTED-LINEAR-SBR25-900mm-RAIL-SHAFT-4SBR25UU-Rounter-Bearing-/251202132300?pt=LH_DefaultDomain_0&hash=item3a7cd0594c), or maybe less here (http://stores.ebay.co.uk/linearmotionbearings?_trksid=p2047675.l2563) if you send the seller a message. I'd go for 25mm since they have one more row of balls than the 20mm rails, so are correspondingly stronger. Having said that either will be a huge improvement on what you have now.

dudz
21-12-2012, 07:08 PM
Wow, China again. After shipping plus import tax, do you think the prices would still be better ?

Jonathan
21-12-2012, 07:14 PM
Wow, China again. After shipping plus import tax, do you think the prices would still be better ?

To England I'm certain they would be, so unless where you live the taxes are even more extortionate, it should be cheaper.

wilfy
21-12-2012, 07:24 PM
Wow, China again. After shipping plus import tax, do you think the prices would still be better ?

just for the record i've had to pay 21.50 to fedex a week after i got my deliveries from china, i'm not sure if it's that much due to the fact it come in 2 parcels

dudz
21-12-2012, 07:29 PM
hmmmm..... I just payed 37 euros taxes for an item from the US which cost 85 dollars.

dudz
21-12-2012, 07:41 PM
I have 45mmx45mm profiles with 10mm T slots. Please could someone point me towards an ebay link that sells the correct T Nuts and bolts for these rails for 45mm profiles. I think the rail bolts need to be M6.


FOUND THEM....thanks

dudz
21-12-2012, 07:53 PM
Ah ha.. probably these : x20 T-Nuts Slot 10 M6 1001 | eBay (http://www.ebay.co.uk/itm/x20-T-Nuts-Slot-10-M6-1001-/221140634498?pt=UK_BOI_Metalworking_Milling_Weldin g_Metalworking_Supplies_ET&hash=item337d024b82)

dudz
22-12-2012, 02:21 PM
OK. These rails purchased...2 linear bearing slide unit SBR25-850mm rails+4 blocks | eBay (http://www.ebay.co.uk/itm/250673108455?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649)

I hope the quality is as good as the ones sold in the UK.

njhussey
22-12-2012, 05:06 PM
You should have contacted Chai directly then you'd have got a better deal!!

Most of the rails sold in the UK are imported from China anyway ;)

dudz
28-12-2012, 09:38 PM
Ok.... I received my Aluminium via UPS. 470mm X 300mm X25mm

I clamped it down to the original bent Vacuum bed (which temporarily straightened it)... planned the new supported rail bearing block mounting holes in CamBam and successfully drilled and counter-bored the holes. First thing I have ever done with this machine since changing the Z axis plate and adding the 2.2kw Chinese spindle. What an improvement so far !
Still a way to go to make it more sturdy, but I am already planning the next improvements to come.

Now... in respect of holes for clamps on the cutting bed.....For now I am going to drill and tap some holes for clamps. (maybe cutting slots later if needed). What size metric holes should I use for the clamps ? M4/M6 ?? and what depth ?