Time to say Hi

[Graeme]

Hi

I currently have no practical experience of CNC, but have always had an interest in using computers to manufacture. The idea of being able to draw something in CAD and then have a machine make it for real, really appeals to me, especially as I am not very artistic.

My day job is as an electronic designer with input into the 3D design of the moulded cases. So I do have a good appreciation of CAD and manufacturing processes. This coupled with my many years of wood working means I now have a long list of items I want to make, but don't have the required tools (or skills) to do successfully.

I have been lurking in the background for about the last year trying to soak up all the information I can. I am now at the stage where I can start to apply this knowledge and have come up with a design that I am hoping to build (well actually design version 5 and counting). To be honest the current design is very much based on Kingcreaky & Eddycurrent machines.

So my plan is to build a CNC router capable of machining all types of wood and hopefully be capable of machining the odd small bit of aluminium. Like a lot of people I am very limited on space and machinery which does add to the challenge of making a good CNC machine.

In time I hope to start a build log and start tapping you lot for answers to the many questions I still have.

Graeme

[EddyCurrent]

Consider this first; do you want a 4th axis at some point ? I would certainly plan for that in your design even if you don't install it now.

[Graeme]

I have thought about the possibility of adding a 4th axis. Originally I was going to shorten the bed to allow the 4th axis to go across the front of the machine outside of the main bed and have an extension bed when not in use. I was not sure if the smaller frame would make for a less rigid structure. So I am currently thinking of having a removable single bed. This could then allow me to mount the 4th axis within the main frame. As home user I don't think that swapping the bed for 4th axis is too much of an issue for me - assuming I ever get to need/use the 4th axis.

[EddyCurrent]

Don't forget to consider the Z travel, you don't want the 4th axis too low down. On my machine I think it would fit on top of the bed if I just wanted to do small stuff.

There's this idea too; http://www.cnczone.com/forums/diy-cn...athe-quot.html

[Ger21]

You might also want to allow for a method of mounting boards vertically at the end of the machine, for cutting wood joints like dovetails, box joints and tenons. With your current design, this could be accomplished with a fixture that mounted to the bed.

[JAZZCNC]

Hi Graeme,

Few things to mention.
First regards the frame then it's 99% ok except It needs bracing at the sides where uprights meets the base.? Because the uprights only connect with small amount of lower frame then you could get resonance thru the uprights. I would brace the ends more or have them extend down lower than bed creating feet and brace between them kind of thing.

Second regards a 4th axis and removing the bed I wouldn't do that on a small machine.? Leveling and skimming the bed parallel to spindle is a time consuming and messy affair and you would have to do this every time you replace the bed which is pain.
Much better to have on the end or have gantry extend past the sides and run down side of machine if longer lengths required.
Having the Rails extend past the end of the bed is an easy way to incoprarate 4th axis and have it fasten to the legs just below the rails so keeping distance to Z axis short.
The other upside to extending rails past end is that you can machine the edges of long boards or oversize material. Or fasten material to the ends enabling dove tailing etc. Extending past the end is very useful at times and add's very little extra cost to machine.
If you extend both ends you can recover the lost bed and use all the bed area.!

Why so tall if your not having adjustable bed and only thinking to cut wood.? The distance the Z axis extends greatly affects the quality of finish you'll get so if your only planning on cutting boards then keep the Gantry/bed distance to a minimum for maximum strength.
It's nice having extra clearence for the odd 10% of times you'll cut deeper material or jobs but it does come with a cost on quality for the 90% of time you won't.!! . . . Unless you raise the material to the cutter.? In which case your better having an adjustable bed.!

EDIT: On looking again and seeing 155mm Z dimension it's not exactly over tall and think the perspective makes it look worse but still some of what I say above still applies if your mostly cutting boards or material less than 50-75mm thickness.!!

Good luck and nice to see someone who's taken the time to do some research for a change.!

[Graeme]

Thanks for the comments - got me thinking again .

The idea of the 4th axis along the side is very interesting. But I don't think I have either the physical space to extend the machine or a design for the Y axis that can pass the X axis linear bearings. So I think I will stick with the current layout and look at the option of possibly removing part of the bed, especially as I had not planned on a 4th axis (but now getting interested).

The ability to machine the edges of boards with a small changes to the design does seem like a good idea. What sort of overhang should I aim for ? I was trying to keep any overhang as small as possible to stop any possibility of ringing.

I have been considering having an adjustable bed, but can't decide if it is better than raising the work piece with a secondary bed.

I think I should start a build log for this design so that I can start asking the questions that are still needing answers. I can then post some more detailed pictures with better perspective and dimensions.

Thanks for the complement JAZZCNC, I hope my research has been along the right tracks (as most of it came from here). As a beginner it is very hard to decide if the available information is relevant to my requirements and if it is also good advice from someone who has real experience. This usually means more googling to see if it makes sense to me.

Thanks again for the encouragement and comments, much appreciated.

G

[JAZZCNC]

The ability to machine the edges of boards with a small changes to the design does seem like a good idea. What sort of overhang should I aim for ? I was trying to keep any overhang as small as possible to stop any possibility of ringing.

You don't need much at all 4-6" will do it as the way you have it already the cutter will partly come past the end of the bed but having that little overhang gives flexabilty for wider things you may want to work on. Also suits 4th axis on end as some times you want to be able to machine the whole diameter of cyclinder. IE flats. on spindles etc.
The overhang at either end doesn't cause any ringing at all because your not actually cutting on it just parked mostly.!

I have been considering having an adjustable bed, but can't decide if it is better than raising the work piece with a secondary bed.

Regards adjustable bed then from experience I can say it's not often adjusted. In use you tend to find a balance that works for most materials but when needed it's priceless.
Secondery bed is ok but got it's own draw backs in that it's fixed to a secondary height or you need several which then takes up room storing.

Personally If your only cutting wood then I'd stick with fixed bed and keep Gantry height to minimum needed. If cutting aluminium and wanting best finish etc then I'd go with an adjustable bed.

As a beginner it is very hard to decide if the available information is relevant to my requirements and if it is also good advice from someone who has real experience.

Yes the theorist's and those that just regurgitate stuff they've read else where but have no actual building or using experience can be a real pain in the arse. Most are giving advise with good intent and do make it clear it's just based on what they've read not actual experience but those that dishout advise like they've done it all really get my blood boiling at times. To me they stickout like flashing bollards but to those new or impatient they come over has Guru's.!
Edit: Must say this forum doesn't have many and those that do don't hang around long.!!

The other problem or gotcha to watch for is getting caught with following or copying one design.? . . . Why because you also copy there problems or Bad decisions regards electronics.!
Much better to look around ask people about any issues they've encountered or would change and what they use machine for.!
The frame and it's design are just one key area but the other is electronics. Good electroincs can make or break any machine no matter how well built or designed. So focus on this at the right time and again Ask those that you see using any components your thinking to use.
Try to avoid any advise from those that have no real world experience with using said electronics and ask the forum about any potential purchases.

From the beggining realise that to do this right doesn't need to cost the earth but it can't be done on the cheap either. Done right you'll build a machine to be proud of and equal machines costing several thousand's more. Do it wrong or in haste and it will cost nearly the same and perform like shit.!!

Good luck .!