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qwertyjon
06-03-2014, 07:02 PM
Hi everyone, after lurking on here for a short while, its time to bite the bullet and get something done about it.

My initial thoughts are to use mdf to make up the framework. Then once I have worked out all the sizes, got it working, made mistakes, and fixed them, I'll stiffen it all up by repalcing the mdf with aluminium/steel plate.

Ideally I want it to be able to cut softwoods, plastics and maybe rarely aluminium. With a bed size of around 700 x 700 x 100.

My first ideas were to use supported rails on X and Y with round rail on Z. Im also torn between leadscrews or ballscrews. Is the extra cash worth it?

Im not after anything that can cut in miles/min, but I also dont think the neighbours will appreciate it being run 24hrs a day.

Not thought about the electrics/motion side of it yet, any advice would be greatly appreciated.

This weekend's task is to come up with a design as a starting point. Im quite lucky to have access to solidworks (albeit only basic knowledge).

Qwertyjon

EddyCurrent
06-03-2014, 10:30 PM
The best and cheapest way to, "work out all the sizes", is to use Sketchup (or Solidworks if you have it) then you can go right to the metal. If you've had a good read on this forum you will see that it's supported or profile rail all round and ball screws. Obviously there are MDF machines with all sorts of arrangements out there and they seem to work but also they are inaccurate, slow, and can't cut much of anything with a decent depth of cut.
Personally I don't have time to waste and neither should anyone else so just go for the right stuff from the outset.
Oh and welcome to the forum.

qwertyjon
07-03-2014, 03:34 PM
Eddy thanks for the vote of confidence, I think I might have those first cut worries. I've never made anything on this scale before.

Is there such a thing as a 'plug and play' electricals available? Im quite mechanically minded but not electrically.

GTJim
07-03-2014, 04:38 PM
To be honest not many of us have done anything like this before thats why a forum like this is important as it allows questions and answers to be posted.
Bite the bullet.

JAZZCNC
07-03-2014, 05:31 PM
Eddy's correct about MDF it's false economy and while yes it may seem good for learning but reality is it's not that much harder to build one in steel and the learning is just the same but without all the hassle you'll have chasing accurecy and flex etc.

Electrics are easy really and with a little guidance you'll do it no problem so don't be afraid. There are a few products out there that make it easier depending on the size of the machine but I won't mention them yet as your many steps away from that yet and it will only serve to cloud the vision.
When the time comes we'll help you choose the correct electrics and guide on how to wire etc but first you need to start with the design style and size plus materials it will be built from. Then other things like linear motion components ie ballscrews, rails etc can be decided then from this lot the electrics can be choosen.

So first step design or Nick some others design then go from there.!!. . . . . . Ask anything your unsure about, no matter how silly you think it may sound ask rather than be unclear and get it wrong.

Good luck.

qwertyjon
08-03-2014, 03:21 PM
Just a quick one for anyone, I presume the bf12 can go either way round, but which way does the bk12 go?

JAZZCNC
08-03-2014, 04:14 PM
Can go either way but like this is most common. 11792
Just a quick one for anyone, I presume the bf12 can go either way round, but which way does the bk12 go?

EddyCurrent
08-03-2014, 08:53 PM
Funny you should say that, here's my recent findings about the similar FK12

http://www.mycncuk.com/forums/machine-building-faqs-problems-solutions/7252-way-round-mount-fk12-bearing.html

JAZZCNC
08-03-2014, 11:12 PM
Funny you should say that, here's my recent findings about the similar FK12

http://www.mycncuk.com/forums/machine-building-faqs-problems-solutions/7252-way-round-mount-fk12-bearing.html

FK bearings are slightly differant but same applies they can go both ways around. Then only thing with FK is that you can only use one side of the flange but which way it fits on the screw doesn't matter.
When I've fitted them I've always found it best to fit the flange to outside of bracket or plate holding then this way it makes removing screw easier.
If you put it on inside it's trapped and makes removing harder and means taking brackets or plates off to remove which then means you have to realign again when replacing. Where if you machine brackets accurate so nice fit for bearing then removing screw for what ever reason is simple and goes back in same place without disturbing anything.! . . . . If that makes sense.??

qwertyjon
09-03-2014, 06:27 PM
As promised, I've been working on my design. I've decided to go slightly larger as it works out at only a few more. So overall size is nearer 1100x1100mm now.

Can anyone point out any obvious faults before I carry on? I've designed it with twin X ballscrews, probably going to be belt driven. I'll apologise now that the screws, don't look like screws. And I've not worked out the Z axis yet. Hopefully its a good starting point though.

The base runs on 20mm supported rail, and the gantry on 16mm. The brackets that I will need to make are out of 12mm aluminium. Will that be strong enough?
11797
11798

JAZZCNC
09-03-2014, 09:47 PM
Can anyone point out any obvious faults before I carry on?

Yes I can point out a few things. The gantry is a little flimsy with just one piece of 90x90 but worse is the connection to the X axis bearings. Relying just on the bolts in profile won't be enough and it will need much more bracing than that other wise you'll get resonance and chatter at the cutter.
I would increase the plate thickness on the ballnut mounts and bearing plates.

Presume those Angle brackets are just for stiffening and your not relying on them to hold profile together, if you are they won't be good enough.

To be honest I would re-think the gantry single profile piece and beef it up a little.

EddyCurrent
09-03-2014, 10:03 PM
A few things pop out for a start.

1. The gantry is not deep enough, it would be better to have two cross pieces and put the ball screw between them. The reason is that the further apart you can put the rails the better, it helps reduce twisting.
2. Are the X ball screws that low down for a reason ? it's regarded as advantageous to have them level with the rails, it looks like you could raise them okay.
3. Most people use 20mm aluminium plate for most of the components.

This is a good diagram to study.

Do it yourself CNC router: Design Considerations, the Gantry (http://www.cncroutersource.com/do-it-yourself-CNC-router.html)

Edit: Dean, I was faffing about with an edit while you posted.

qwertyjon
09-03-2014, 10:20 PM
Jazzcnc - thanks for your comments, I was planning on using the proper profile jointing bolts with the angle for support. If that makes a difference? I did think that using 12mm plate was a little thin. So I'll redesign with the 20mm that eddiecurrent suggests. I'll have another think for the gantry too.

Eddiecurrent - thankyou also for your input. I'll have another look at the gantry. The X ballscrews were put there for convenience to attach to the profile. If there are benefits to having them level then I'll definately lift them. Thanks for the site link too.

Finding this forum has already probably saved me a fortune in redesigns, I appreciate the help im getting.

qwertyjon
10-03-2014, 12:06 AM
Version 2 - 1. Adjusted to use 20mm plate. 2. Raised X ballscrew's, inline with supported rails. 3. Doubled up on gantry crossmembers. 4. Added extra profile on gantry legs. 5. Added plate inside the 'legs', attaching to legs and ballnut mount.
11801
11802
6. Gantry bf/bk mounts considerably larger, encompassing both crossmembers, and legs.

EddyCurrent
10-03-2014, 11:29 AM
Make sure you have enough room under the gantry, between it and the bed, it looks a bit tight as it is, once you get the spindle hanging off there and some tooling in your not going to have much depth for the stock.

qwertyjon
10-03-2014, 11:34 AM
What sort of distance should I expect between spindle and tool tip?

EddyCurrent
10-03-2014, 11:47 AM
Not sure exactly what you mean but some people have it so the collet of the spindle, without any tool in it, comes right down to the bed. In my case the largest cutter I'm using is 50mm long so the distance from the end of my collet to the tool tip will be about 70mm. Then I will be using sacrificial boards on top of the bed and in some cases a small vacuum clamp on top of the bed, then my stock might be up to 50mm thick, maybe more, so the spindle has to rise above all that with a 50mm cutter in the collet. Mine is working out to have a 190mm travel on the Z axis.

qwertyjon
10-03-2014, 12:49 PM
You did a good job of deciphering my post. Thats exactly what I meant. Thanks

Fozz84
14-03-2014, 12:24 AM
qwertyjon; If your near Torbay in South Devon, I am wanting to build a machine, the cost MIGHT be reduced if we order the aluminum together? can't do it until the end of the month though!

JAZZCNC
14-03-2014, 01:44 AM
qwertyjon; If your near Torbay in South Devon, I am wanting to build a machine, the cost MIGHT be reduced if we order the aluminum together? can't do it until the end of the month though!

Erm I'm no geological expert but last time I looked Devon and Scotland where several hundred miles apart.!!. . . . Thou with all the floods recently suppose we could have had a land slide. . :hysterical:

qwertyjon
14-03-2014, 02:31 AM
Sorry fozz84, like jazzcnc says, we are a long way apart, especially as im on the north coast

qwertyjon
14-03-2014, 02:34 AM
Just a quick update. The extruded aluminium has proved to be a non starter for my tiny budget. So im currently working on version 2. Might be a while though the wife (I mean life) keeps getting in the way

qwertyjon
14-03-2014, 02:23 PM
My latest design has the supported rails sitting sideways. Is there a side loading limit for 16mm and 20mm supported rail? Ive got a rough figure of 100lb (45kg ish) for the 16mm rail from another cnc site. Does this sound realistic?