View Full Version : BUILD LOG: I'm going to need some help.

31-10-2012, 03:03 PM
I've decided to build a metal CNC machine to replace my MDF one.
I'm going to reuse the supported rail, ballscrews, stepper motors and drivers off it. This means a single ballscrew down the middle of the long axis(I'd call this the Y but I know some people call it the X).

This is what I've come up with.
The aluminium extrusion is a mix of 45x45, 45x60 and 45x90. The plate is 20mm. The rails are SBR20 and the ballscrews are RM1605.
The dimensions are 1180mm x 756mm
Is it any good?

Whilst I have access to all sorts of wood working tools and machines the only one that'll be any use building this is the drill press. So I'm hoping someone will be able to machine the plate for me when the time comes?

Thanks :)

31-10-2012, 04:57 PM
How good is the machine you have at the moment? I have read that some people use the machine they have to help manufacture the new machine. If your machine is accurate then with light cuts you may be able to do the machining yourself rather than pay someone else.
Will leave the critique to those with the experience as I am new to all this myself.

31-10-2012, 05:18 PM
ah well, it was never actually functional :highly_amused:
I decided it would be better to spend my time, energy and money on something better.

31-10-2012, 05:51 PM
Why wasn't it functional? Reason I asked is because I had started to manufacture an MDF book build machine before I found the forums & had already progressed a long way before I started to read some of the downsides to them. Because of the stage I was at the advice from the forum was to finish it so I could firstly gain a bit of experience using the machine & the software & secondly because it might be possible to use it to help with the next build. I was advised to buy electronics that I could migrate to the next one so I wouldn't have to buy them again.
You already have better components than I have if you have supported rails & ballscrews. Can't be that far off complete if you already have all the components so may just be worth finishing.

31-10-2012, 07:30 PM
It was almost finished with skate bearings and thread rod. But it didn't feel anywhere near steady or sturdy enough so I got the ballscrews and rails. I started fitting them but it still felt too flimsy, so here I am.

I also have 3.1Nm Nema23 stepper motors and 542 drivers which I think are fairly good.

I was thinking of turning the remnants of the MDF one into a 3d printer since they look like fun.

31-10-2012, 09:12 PM
In general what you've drawn looks like a pretty strong design, but it's let down by only having one ballscrew on (what you have defined as) the Y-axis. For the width of your machine you really should use two ballscrews, one on either side of the gantry, particularly if you want to cut metals. Currently when the Z-axis is at either side of the gantry (so the limits of the X-axis) and a force is applied parallel to Y, you will get significant deflection. If the bearing spacing on Y is increased, this will help but you would have to increase it a lot to make a significant difference, which is clearly undesirable as you would loose travel.

Since you need a second ballscrew I strongly advise getting RM1610 and selling the old one since you will get much better feed-rates with the higher pitch screw.

The Z-axis looks good. You could make the plate on the rear thinner, say 10mm, but it's probably not worth it if you're going to get all the parts cut from a 20mm sheet anyway.

01-11-2012, 12:05 PM
Thanks for your input Jonathan.
Do you think the "significant deflection" would be a couple of millimetres or worse than that?
I wonder if I could make do with one ballscrew to start with and replace it with two later on? Moneys pretty tight at the moment.

As for the frame design, does having the rails directly under the gantry improve the rigidity, compared to other designs I have seen with tall gantry sides? like this:
7261(not an actual design, I just deleted some bits to show what I mean)
Building it like this would save money but would it compromise the strength of the design?

01-11-2012, 02:19 PM
Do you think the "significant deflection" would be a couple of millimetres or worse than that?

Possibly, it's hard to calculate an actual figure as it depends on so many factors. To an extent you can minimise the deflection to an acceptable level by reducing the depth of cut and thus the cutting force, but there's clearly a limit.

I wonder if I could make do with one ballscrew to start with and replace it with two later on? Moneys pretty tight at the moment.

It's not uncommon to do that, although bear in mind the piece of aluminium on the bottom of the gantry is wasted when you do change.

As for the frame design, does having the rails directly under the gantry improve the rigidity, compared to other designs I have seen with tall gantry sides?

Your first design with the very short gantry sides is far better than this concept since the gantry sides are effectively replaced by the main frame, which is significantly stronger and can be made so since it is stationary. If you want to save money consider using steel box section for the main frame instead of aluminium extrusion.

01-11-2012, 02:43 PM
What is it you want to do with the machine? Might be that the MDF machine will be up to a lot of what you want to do. If it's practically finished then completing it & using it might be an option especially if money is tight. That way you could use the machine to generate some income for the second build. Sorry if it sounds like I keep going on about this but that was the advice given to me by some very experienced members of the forum. I know a guy that has been using an MDF book build machine for the last 9 months & although not run on a regular basis it has done everything he has asked of it so far, he is very happy with it & says it's more than payed for itself.
I was like you, started building & then discovered they weren't as good as I thought they would be so started looking into building a different machine before I had finished. After speaking to a few people on the forum I was advised it would probably be best to complete it because of the stage I was already at. That's what I am now doing, I already know it won't do everything I want it to but it will get me started a lot quicker than starting from scratch so is probably the best option.

01-11-2012, 08:35 PM
I think perhaps you've convinced me to persevere with the MDF one, although a nice strong metal one is still my ultimate goal. I want it for cutting plastic and wood for custom electronics/computer cases as well as model making. Although I'm sure I'll find the ability to machine aluminium handy as well. :)

I think I'll stick with aluminium extrusion, since it seems a lot easier to work with than steel.

Thanks for the help, both of you. I'm going to gradually buy bits for metal one, now that I know the design is sound. :D

01-11-2012, 09:26 PM
Just passing on the advice that was given to me, I had concerns about the MDF machine even though I knew someone who had built one & was using it. As I had already bought everything I needed except for the electronics, all the parts for the machine were cut & drilled plus a fair bit of the machine was built I was advised to make sure any electronics I bought could be migrated to another build so I wasn't wasting any money & then just get on & finish it. Yes it is costing me some of my time but that is all & I can afford that just now. It is also giving me time to learn more about machine construction for the second build. I can slowly buy the materials I need for the next machine & just store them away until the time is right. Once the machine is built I can then start learning how to use both the machine & the software I am unfamiliar with while I finish collecting what I need for the second build, in fact right up to the time where I need the parts lol.
I can still recycle the MDF at that stage if I find something else to use it for.

I know that won't suit everyone but it does suit me at the moment which is why I am doing it. If you decide to complete the machine don't forget that there are a lot of very knowledgeable people on this forum so don't be afraid to ask any questions you may have about completing it. Best of luck what ever you decide to do.