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Hopey
13-11-2014, 09:36 PM
Hi I'm a newbie here and to CNC.

I've read up on design principles and think I have a fair understanding of the moments these machines go through.

I basically need some help with design, I want to build a machine with a cutting size of around 900 x 400 to build guitars on. It'll be cutting hard wood and doing a good few hours a week hopefully.

I've seen a few build in MDF and thought could I build in maybe ply (I'm not a fan of MDF) or would it really need to be welded steel for hard wood like maple and ash?

I have a basic idea of my design but I could do with knowing if the idea of a ply build is just silly before I start drawing.

Cheers Kenny

EddyCurrent
13-11-2014, 11:15 PM
My advice would be use metal for the build, wood of any sort would be a waste of time and money. You need more accuracy and maybe more important, repeatability, and I do not think you will achieve that with a ply or MDF built machine. Think of the accuracy required for a neck pocket as example or maybe you want to cut an accurate rebate for binding.

Christian Knuell
13-11-2014, 11:33 PM
Hi,



I've seen a few build in MDF and thought could I build in maybe ply (I'm not a fan of MDF) or would it really need to be welded steel for hard wood like maple and ash?

Plywood is even worse than MDF because MDF at least does not warp and bend too much just because of temperature or humidity changes.
Steel is not necessary for hard wood but I'd at least use aluminum extrusion.

Christian

EddyCurrent
13-11-2014, 11:38 PM
Plywood is even worse than MDF because MDF at least does not warp and bend too much just because of temperature or humidity changes.

I'm not sure I agree with you regarding plywood being worse, good birch plywood I mean, but I do know that among other things moisture makes MDF swell. Also if there's that much moisture in the air then the hardwood being cut will also be useless, especially for guitars.


Steel is not necessary for hard wood . . . but it's a lot cheaper than aluminium and ideal for the base.

JAZZCNC
14-11-2014, 01:47 AM
Plywood is even worse than MDF because MDF at least does not warp and bend too much just because of temperature or humidity changes.

No sorry can't agree on this. Unsealed MDF changes shape if you so much as show it a cup of coffee let alone any decent amount of moisture. Ply wood will take much more moisture before swelling.

BUT to IMO both have only two places in CNC.? . . .Spoil board or to keep the workshop warm.!!

Steel is cheap and easier to work than people realise. Profile is fine but to get the best from it you need all the connection elements, T-nuts etc, and this makes it much more expensive. It's also harder to work than people realise, it's awkward drill/Tap and unless slots used then it can be difficult for mounting things too it with out adaptor plates.

Combination of steel and Profile works well IME, gives a good balance of strength and ease of build without getting silly expensive.

Hopey
14-11-2014, 09:08 AM
I've used MDF for templates which it's great for but does deform and swell if it gets wet. Decent marine quality ply wouldn't have this problem so I had thought of using a combination of that and hardwood to build a strong structure but it could just become a bit cumbersome.

I can weld and it has to fit in a shed so steel makes more sense when I think about it.

I'm thinking 1" box section for the main frame.

Best get drawing.

Neale
14-11-2014, 10:12 AM
Let me add my twopennorth as someone who has built and used an MDF CNC router, essentially to the JGRO design. There aren't many people prepared to admit that...
I have a cutting area of about 800x400, from memory. It uses skate bearings on steel tubes and threaded rod. On the plus side - it works. On the down side - only just. It's difficult to get a flat bed, to adjust the bearings and keep them adjusted, and generally to maintain any kind of consistent accuracy. There are better MDF designs but I doubt that they will entirely remove all these problems. As Jazz has said, show this stuff a cup of coffee and it distorts. Take the coffee away, and it will sulk and distort again, but probably not back to where it was. Warm/cold/damp/dry - any change in weather and you will be re-tweaking. All that, actually, might be bearable except that you have to keep cutting speeds so low to avoid major structural distortion - or failure - that big jobs can take hours rather than minutes. OK, I use threaded rod as leadscrew material which limits X axis speed to about 800mm/min, but frankly the thing couldn't take much more anyway.

As far as accuracy is concerned, I cut a series of interlocking 9mm ply panels for an architecture project and had reasonable repeatability, although not absolute accuracy - that is, I cut some samples, tweaked the dimensions slightly, and then cut a series of pieces that fitted reasonably well. It works pretty well for engraving, as long as you can level the work.

I'm halfway through a build of a steel framed machine using profile rails and ballscrews. Is there a message in that?

JAZZCNC
14-11-2014, 12:02 PM
I'm thinking 1" box section for the main frame.

No 50x50x3 Minimum for a decent strength machine. Steel is cheap if bought in full length sizes so don't compromise the machine with 1" for the little extra 2" would cost.

EddyCurrent
14-11-2014, 12:39 PM
I'm thinking 1" box section for the main frame.

This machine was built for hardwood cutting, similar size to your proposal, it works great and is very accurate.
First part of the thread is just random ideas, it should give you some idea of what is required.

http://www.mycncuk.com/threads/6565-Ready-Steady-Eddy

The frame; http://www.mycncuk.com/threads/6565-Ready-Steady-Eddy?p=52425#post52425

Hopey
15-11-2014, 01:29 AM
Thanks for the input guys, I was thinking I would build a bench in the shed and simply sit it on that or bolt it down but now I'm thinking it needs a solid frame too.

Great build thread Eddycurrent, I'm a bit dyslexic so it takes me a while to read it all and take it all in. I've skipped over a lot of the electronics bit for now but finding the epoxy levelling really interesting.

Bear with me and I'll finish the reading and get some drawing done.

I was looking at Chinese rails and lead screws on ebay, are the Hiwin type worth the extra cash?

Thanks again for your assistance.

Ger21
15-11-2014, 01:36 AM
It's very possible to build a decent machine from wood, contrary to what you're hearing.
But it won't be easy.
For one, I've never really seen any plans for a "good" wood construction machine. Just about all plans for wood machines are designed to be easy to build, and inexpensive. Neither of which lend themselves to good machines. Building a good wooden machine is not easy, and requires a lot of knowledge, skill, and time.

You also mention that your on a budget. Trying to build an inexpensive machine is another way to end up with a poor machine. Good machine require good components. This is especially true of a wood machine, where high quality components can make up for inferior construction. Anywhere you try to save money, the quality of the machine decreases.

If you can weld, then your much better off with steel. It'll be faster, cheaper, and stronger than building with wood.

irving2008
15-11-2014, 05:51 AM
And if you can't weld, buy/borrow/steal a cheap stick welder and some steel scraps (ask to rummage in the bins of a local fabrication company), watch a few YouTube videos and teach yourself to. Its time well spent to gain a new and useful skill.

Edit: I see earlier you said you could weld, so no brainer then!

Sven
15-11-2014, 07:54 AM
When Isombard Kingdom Brunel proposed to build a ship out of iron, everyone said that would be ridiculous. It is common knowlege that iron does not float.

I feel that some similar reasoning is going on in most of the replies here.

Have any of the poster saying that wood will not work actually tried building a good router from wood?
I've been working on one for quite some time and I feel that it should be possible to get a wooden machine to work aluminium.

But it is not the easiest route to take.
Then again, people suggesting to go with steel also say it is "easier" because they are used to working with steel. But OP is used to wood.

I think that if you want to build a good machine from wood, this is what you need to do:
- Build a torsion box for both the bed and the gantry, at least 25 cm width for the gantry
- Use Bamboo or mahogany marine plywood
- apply epoxy to the sheets before working it, making sure no excess builds up on surfaces
- apply epoxy to the edges after cutting and during assembly
- use a biljard table as a flat surface for glueing the torsion boxes

All of this is not "easy" nor "cheap" but for a wooden person may be easier than going with steel...

Hopey
15-11-2014, 11:04 AM
I do like the torsion box idea, it looks like it could be fun to play about and build something unusual and cool with but for now I have a whole other mountain to climb. I have to learn to build, set up and operate this machine.

I've not done any welding in a few years but I work in a brewery and we have a TIG plant that no one can use, since there's always some fabrication job needing done I've enrolled in a welding course. So building this will be practice, it was even suggested I could built it in stainless but that seems just a hint over the top.

EddyCurrent
15-11-2014, 11:32 AM
It's very possible to build a decent machine from wood, contrary to what you're hearing.But it won't be easy.

I watched a TV prgramme this week called "Wheeler Dealers", they bought a car from the US, a 1969 Carmen Ghia. There was not one bit of rust on it, and as the presenter said, in the UK there is no way that could happen due to the weather. I think it's the same with these wooden machines, most I see are in the US and not subject to UK atmospheric changes.


. . .Then again, people suggesting to go with steel also say it is "easier" because they are used to working with steel. But OP is used to wood.

I found steel and aluminium to be no harder to work with that wood, in fact steel is easier because mistakes are easy to repair with a welding rod. Aluminium is like using hardwood, I used woodworking tools for all my milling and cutting operations on it.

Sven
15-11-2014, 12:02 PM
most I see are in the US and not subject to UK atmospheric changes.

Building it using epoxy will completely seal against moisture.

The mentioned situation on wheeler dealers also has something to do with the way cars were painted back then...



in fact steel is easier because mistakes are easy to repair with a welding rod.

The same goes for Wood and epoxy, when used together from the start.

(I have a wood-epoxy boat, with wood-epoxy fuel- and water tanks and very much used to working with the stuff.)

Hopey
15-11-2014, 12:30 PM
I'm loving these ideas. I use to look after our water ski racing boat years ago so I can work with epoxy I've even seen boats made from balsa wood, epoxy and glass fibre. I could be tempted to do an interesting build from unusual materials another day. Keep these ideas coming my imaginations going wild here.

Eddy' did you find any drawbacks in rigidity across the y axis with your open ended design? I was thinking it had to be a box type design but you have 100x50 box section on the X axis and nothing at the ends on the Y axis. I like this idea!

Ger21
15-11-2014, 02:48 PM
I think it's the same with these wooden machines, most I see are in the US and not subject to UK atmospheric changes.

Here in Michigan, we're surrounded by water, so we can get very high humidity in the summer, and very dry and cold winters. I have a wood machine, and it's 11 years old. It's no different than the day I built it. As Sven said, you just need to seal it properly. The problem with 99% of wood machines, is that they rarely get sealed and finished properly, and are usually poorly engineered to start with.

I'm currently working on a 4x8 dual spindle wooden machine. It's very complex, with lot's of laminated materials, bonded in phenolic for rail mounting surfaces (cnc machined straight and flat), and lots of aluminum for mounting surfaces (motors and drivetrain components) and brackets. And lots of epoxy.
It's a lot more work then building with steel, but I find it easier and far more enjoyable than working with steel. But it definitely takes a lot longer, and requires a lot more thought when designing.
You can easily weld two pieces of steel together at a 90 angle, and get a very strong joint. Try to do the same with wood, and it's much more difficult, and will almost always be a weaker joint.

JAZZCNC
15-11-2014, 03:17 PM
Wow slow down lady's no one actually said it wasn't possible to build a good router from wood.!!

I personally said wood and inparticular MDF is not a good material for a CNC machine which it isn't.. . Period.!. . . . . HASS build routers and Mills but they don't make them from MDF or Wood do they.!! . . . I never said it wasn't possible and having worked with wood all my life I know it's possible but I also know it's far from ideal and much much more work than steel.
Also carry's with it a much higher potential for failure and dissapointment even for someone compleltely used to working with wood and tooled up.

Ger is correct that most Wood based routers fail because of poor engineering or design. Often they are also compromised by the type or quality of components used and most that take the Wood route do so for budget reasons so use inferior components which just greatly compounds the issue.!
I've seen many 1000's of good builds from steel/aluminium but I've seen relatively few Good successful Wood builds.!! . . . . . For sure This doesn't mean they are not being built from wood just that they rarely last very long or are successful so don't get seen.!

JohnHaine
15-11-2014, 04:18 PM
There is a building product made to seal wood that has rotted to avoid having to replace it, for example in window frames. Here is a link:

http://www.screwfix.com/p/ronseal-wet-rot-wood-hardener-clear-500ml/63540

MDF soaks it up like a camel at a waterhole, and it's surface gets a lot harder. It dries quickly. I would think if you bought mdf and let it stabilise, then treated your components with this stuff, and even with West System epoxy for good measure after assembly, it would all be a lot less sensitive to the humidity level.

EddyCurrent
15-11-2014, 06:45 PM
The OP has to decide which way to go, I know what was best for me, plus, I only wanted to build the machine once.

Hopey
16-11-2014, 05:52 PM
So, it seems that it would be possible but not on budget and maybe not advisable.

I too only want to build the machine once so steel it is then.

EddyCurrent
16-11-2014, 07:03 PM
I too only want to build the machine once so steel it is then.

Good choice.


Eddy' did you find any drawbacks in rigidity across the y axis with your open ended design? I was thinking it had to be a box type design but you have 100x50 box section on the X axis and nothing at the ends on the Y axis. I like this idea!

I've nothing to compare it against but I don't think it had any drawbacks in rigidity, here's some figures; http://www.mycncuk.com/threads/7155-stiffness-measurements-cnc-mk3?p=56572#post56572
Of course there's nothing to stop you putting something at the ends.