Thread: Proposed CNC router build

There is no reason that 2 (or more) separate cutting heads cannot be mounted on the machine, just use different home points for each cutting head.

A Rigid steel base is a good idea.
An ally gantry can be a 1/3rd the mass of a steel one and as mass is a factor then ally is far preferable.

Theres a few forums around on cnc stuff
here is 1

Originally Posted by echnidna

There is no reason that 2 (or more) separate cutting heads cannot be mounted on the machine, just use different home points for each cutting head.

I like that idea

I agree Steel Base and ally gantry you want no flex at all if possible as for moving it yep some casters that can take the weight will make life easy.

I cant lift mine without the wifes help and she strains, we cant move it that far.

Xylotek Kit yep good call but ain't sure if you will need the 425oz Steppers from what I have been advised bigger isn't necessarily better but Rod will no doubt chime in on that.

But Otherwise


Sean

[*]Very rigid

Rigid is good.
[*]Steel base, with alloy Gantry for excellent rigidity - I have thought of using a steel gantry, and would like to know if it is practical with the below rails and motors. Is the rigidity of a steel gantry much better than a good sized alloy design?

Steel is a lot more rigid than aluminum but it is weight that is the problem. There are no moving elements in the base of a gantry router so to reduce cost and have rigidity steel contruction is preferred.

If I use a premade linear slide for the Y axis, how will this effect the gantry requirements?

I assume you mean commercial linear bearing. If so this the the way to go.

[*]Linear guide rails from homeshopcnc

Try ebay as you quite often get good deals. Also have a look at Kelling as they have reasonable priced rails. I can give you a link to a supplier in China if you are interested.


- I notice many people use two bearing blocks on the one X axis rail. Is this preferable?. It obviously reduces travel compared to two rails running parellel on each X axis side. Which is preferable?

Two rails is extra cost and is not necessary. What you want is to reduce the forward and back pivoting on the gantry and that is why we run two trucks each side.
[*]Rolled ballscrews.


[*]Approx 910mm long (X), 610 wide (Y), 310mm high (Z) cutting area

The Z axis is quite high to most home built machines. Extra height in the gantry means more leverage so think about that decision.
[*]Xylotek stepper system with 425 oz.in motors.

Motor selection is difficult. Larger motor usually means slower machine but lots of factors come in to play. Your choice for this style of machine is about right but you might get away with 269oz.
[*]It is planned the gantry will take both a low speed and high speed spindle so it is suitable for timber and aluminium.
I also have a dremel I plan to use.

Sorry but my opinion is throw the Dremil in the cupboard and keep it for hand held use. Dremil bearings are mounted in a rubber sleeve and will not deliver the accuracy you expect from a CNC machine. Power wise they are down as well and a good variable speed die grinder will cut the materials you mention.

[*]I plan to sit the machine on a bench which is on wheels. It would be good to make it easily go onto a ute for transport, but I reckon it would be way too heavy to handle?

As said it will be very heavy when you are finished.
[*]Ready for the addition of cooling fluid at a later date if required. Maybe this could simply be a tray which sits ontop of the deck, connected to a pump when needed?

Do a search on Fogbuster. You might be able to build a similar system yourself. We also use an aquarium pump for blowing cold air and clearing the swarf. Cost about $100 and very quiet compared to a full compressor. Noise is a factor with these machines. Imagine standing next to a router which operated continuously for 30 minutes. The die grinders are a little quieter but still annoying.

Obviously there lots of ways you can do this and everybody has their own ideas. You will notice that there are common components to the better machines and this is no mistake but don't let convention stop you from experiementing with new ideas. A bridge gantry is something you might want to look at if you are after more rigidity. On the same theme a moving table will be more rigid than a moving gantry. I am not saying to do these designs but it might be that you haven't seen these styles yet. Enjoy the journey.

I assume you mean commercial linear bearing. If so this the the way to go

Yeah, I was looking into the commercial linear bearings with integrated ballscrew. That way the gantry could be one of these units bolted directly to the vertical peice which secures up from the x axis. I am having issues with getting the weights of them though.

Rolled ballscrews.

Do you know of suppliers with reasonable prices for new?

The Z axis is quite high to most home built machines. Extra height in the gantry means more leverage so think about that decision.

OK. I will try to keep it as low as it is required. I am only guessing how big I might need it, so it is no big deal.

2690z V's 425oz motors.

What percentage speed difference could I expect between the two types of motors?

Sorry but my opinion is throw the Dremil in the cupboard and keep it for hand held use. Dremil bearings are mounted in a rubber sleeve and will not deliver the accuracy you expect from a CNC machine. Power wise they are down as well and a good variable speed die grinder will cut the materials you mention.

Fare enough. Pity cause it is a great tool


Thanks Rodm

Two things, definetly put the dremel in the cupboard, go out and buy an ozito 1/4 router, there like 49 dollars and history has proven you will get approx 100 plus hours, I got that and more on mine. The ozito also comes with all the little adaptors which allows you to run 1/8 bits as well "perfect for engraving etc"

Hey rod, do you still have that photo of the machine with x y and z from overhead. You showed me it ages ago, perfect for routing designs into floor boards etc. If you have it post up a pic as well, gives the guy some more ideas.

Steel and ally is the ultimate option, mdf works great too, but the more weight in your base frame means more sturdiness and less flex, my base frame is probably about 80kgs total. And when the router is carving up through jarah etc, theres no loss of motion or accuracy through flex of the materials.If you want accuracy and we are talking here down to .1mm and better then more ridigity is required.

For info what Ive read the mdf designs using allthread and spring washers for backlash can cut accuratly to 1-2mm, which is pretty good, better than anyone on this board could do by hand. But 1-2mm is not accurate enough when you are engraving names into plaques and mirrors etc. This is the biggest concern when waying up the pros and cons.

Ask greg (think it was greg) to post up his test on his machine where he made a ruler. Difference between ballscrews and allthread.

As far as heights of Z are concerned, yes rod is correct the more height you go the more possibliity of flex, I have 300mm of z axis travel, but I also wanted to be able to do 3d sculptures and have a A axis with a rotary table to turn the jobs. Example. Imagine making a 3d model of your hand. Full and complete no flat sides. Thats my goal

Steve

Hi Steve,
Sorry I don't have pictures of Joe's 3 axes overhead machine.
Good point about the extra Z axis height though and if you do plan to add a rotary table then the extra height is needed.
There are a lot of MDF machines out there delivering 0.1mm accuracy. The Joe2006 design uses a torsion box and is quite rigid for a MDF machine. If you use acme thread rather than allthread it helps these machines quite a bit both in accuracy and speed.
My thinking is that I takes the same amount of effort to build steel/ally as it does to build it from MDF so for the extra dollars you will have a machine that is far more rigid and last a lot longer. You can also use coolant on the steel/ally combination.

Hi Tony,
Are you talking actuators when you say integrated rails and ballscrew. If so then a new THK actuator is around $3,000 each as a guess for 600mm travel.
I have been lucky and got new units on ebay for $400 Aus landed so try there first. Actuators are great for Z axis but on a large machine that you want to push through aluminum I would think rails and ballscrew are a better option.

I am a back yard builder without an engineering degree so I don't know how to compare motors. I do know that stepper motors have full torque at standstill. As revs increase the torque drops off dramatically and my experience is that on a Xylotex board which is limited to 24 volts any stepper motor is only good for about 300 RPM. The problem with 425oz and larger steppers on a Xylotex is that there are not enough amps able to be passed across the board to take full advantage of the larger motor. 425 will deliver more torque than a 269 at lower speeds but the 269 will rev higher as the max2.5 amp of the Xylotex board is well suited to the 269. Basically the 425 will starve for amps at the higher speeds. I hope that is a good enough explanation from a layman's perspective.

Proxon are a far better choice than Dremil for a small CNC spindle but for my hard earned the die grinder will be able to do what a small spindle will do as well as doing the heavy jobs.

What do people think about minimising the noise produced from the machine, apart from good bearings?

I have thought about putting a clear perspex cover over it, but to reduce noise it would really need to have eggcarton type foam on the inside. This would make it not clear. Maybe foam on the side, with a clear lid?

The other thing to consider is cuttings would get stuck to this foam.

Any thoughts?

The noise comes from the router and the cutter. The CNC part of it is like a feint orchestra - sort of a whining changing pitch.
I built a full hood on one of my machines and it did reduce the noise considerably. Apparently the egg carton thing is a myth and just having different density materials and a barrier to the sound is all that is needed. Noise doesn't travel well around corners.

The down side is that the dust is trapped and gets all over your running gear - not good. Also access to your machine to mount the job is restricted so that is something you need to address as well. I have seen a very neat design with a polycarb enclosure that hinges from one side at the top. Gas struts were used and the cover lifted high enough so that you didn't bump your head when mounting the job. Sometimes I cut a job on a long board and an enclosure would prevent me from hanging the material out both ends of the table.

A lot of commercial machines are built in a separate room or the room is built around the machine. If you can make a small area partitioned off in your shed then I would think this is ideal.

Good to see you are thiking about all the issues in your design stage.

So now I have to incorpirate a vacuum attachment to integrate with the polycarbonate lid which is attached via hinges and gas struts, and can be easily removed so it doesn't interfere with long items

It does seem that there are quite a few things to consider

Tony it is your build so take it as far as you have patience and funds. For starters you only need the basic machine so as long as you have thought about it in the design stage the fruit can be added later.

For a first time builder I would suggest you stay with the conventional gantry router design.

Thanks Rod. My last comment was not meant to come accross as negative. So many options, finite amount of funds.

I will try to make it easy to incorporate additional features later on.

My brother in law wants it to handle a full 1200X2400 sheet

That can be for later if I decide to tackle a rack and pinion design...

Just before Xmas I helped a local sculturuer assemble this beast he imported from China. It will handle 2500 by 1300 by 460 and the gantry had to be lifted by a block and tackle. A crane was used to get machine in his back yard and you need a big workshop to house it. Note the large Z axis capacity which was a special for sculpturing.
It is a really nice machine and has an Italian VFD spindle.
Now that is something I would like parked in my shed.

Originally Posted by AV Elec

T

My brother in law wants it to handle a full 1200X2400 sheet

That can be for later if I decide to tackle a rack and pinion design...

Then for future reference make sure you take a good look at the MechMate

http://www.mechmate.com/

Greg