My first project: A fast router...

[Boscoe]

So I have been interested in making a CNC machine for at least six months now hence my membership of these forums. I have been thinking of this design for the past month and have had it rolling around in my head playing with different ideas. So far this is what I have come up with.

http://i550.photobucket.com/albums/ii406/geowal19/CNC_CHASSIS_RENDER_1.png

It's 800mm long and 600mm wide - I'm aiming for a cutting area of about 650 x 450. It's small compared to some but I want to keep it very strong so I've used 50 x 50 x 3mm box steel and have welded it together instead of aluminium and bolting. I want to use two 1600oz Nema 34 motors on the X and one on the Y for speed and accuracy. I will also use a very high power spindle to ensure my fast feed rate.

This build log is going to go on for a long time purely because I'm a student and don't have any money so I will be doing this in dribs and drabs however I hope to have it finished just after Christmas where I can get everyone to buy me parts for it!

The build so far...

http://i550.photobucket.com/albums/ii406/geowal19/Photo10-08-2013173501.jpg

http://i550.photobucket.com/albums/ii406/geowal19/Photo10-08-2013173534.jpg

As you can see the welds aren't that great on the one at the back as I haven't done any welding in years and so it took a few goes to get some neat welds like the one below.

http://i550.photobucket.com/albums/ii406/geowal19/Photo10-08-2013173519.jpg

I am hoping to finish the frame off today.

I also need some opinions on how to do the gantry. I want to just have a peice of 100mm square box steel resting on the carriages spanning the rails but I can't really decide where I will mount the rails on the gantry like one on the side and top or both on opposite sides etc.

Thanks
Boscoe

[Boscoe]

I managed to finish the welding today I haven't got the grinder out because I don't have any ear protection currently.

http://i550.photobucket.com/albums/ii406/geowal19/Photo11-08-2013133801.jpg

[JAZZCNC]

That what I like to see a man getting on with it and not talking about it. . :applause:

Couple of suggestions.! Put some triangle plates on those upright legs to support them.!! . . . I know your thinking is he on drugs this things built like brick shit house but When machines cutting you'll be surprised just how much those legs resonate and this will transfer thru the gantry and down to the finished cut quality.

I'd also do something on the inside to help keep the frame square, either with similar triangulation braces or plate with holes in each corner then threaded rod between to pull square.

Because you have welded the top rail box section it means your linear rail mountings are going to have to be cock on parallel because you have no adjustment. It also means your top rail surface or plane is fixed so again if you have any discrepancy between each side it will be difficult to get out.
If you bolted it to plates then you have a lot more freedom to shim and adjust into parallel and same plane. There are ways around this like Epoxying the top rails so they level to each other but this is more involved. Depends what you plan to do with the machine but building in adjustment helps greatly with setting up.

[John S]

Motors are far too powerful.
1600 ox in on a 34 will have a hell of a load of detent torque to over come which in turn will slow the machine down.

Very common mistake in that bigger is better.

For the travels you are talking a 3 or 4 Nm type 23 will move far faster than the 1600 motors.
If you want to go fast get the highest voltage drivers you can, usually 80 volts and run them at 50v AC rectified and smoothed with a big cap to get about 72 volts DC out.

[JAZZCNC]

Motors are far too powerful.
1600 ox in on a 34 will have a hell of a load of detent torque to over come which in turn will slow the machine down.

Wow only looked at last picture and didn't read first post.!!. . . . . Bloody hell massive OTT like John says. At this size 3Nm on 10mm pitch screws with 70Volts and it will fly.
When you say you want to cut fast, what exactly do you want to cut.? The material and tool used is often the limiting factor regards speed and most machines will travel far faster than the material or tooling will allow.
Just having a high powered spindle isn't always enough and what exactly do you call high powered.?

From the fact you where going to use 1600Oz shows me a few things.?
1: You've been on the American sites too much. . .Lol and . . . 2: You haven't done enough research in this area.

I suggest you post your intentions and desires then we can help save you from buying the wrong components.
Like John says It's common mistake regards motors but it will have a big affect on performance, same goes with ball-screws, bigger is not always better. So post what your thinking to use and we can help steer you in right direction and suggest you don't buy a thing without asking unless your absolutely sure it's correct for your needs.

[Clive S]

There are ways around this like Epoxying the top rails so they level to each other but this is more involved..

I sort of made a similar frame and used epoxy like others have done on here like this:-

94119412

The bridges from one rail to the other is to allow the epoxy to self level.
The Epoxy is Wests System 205/109 very slow setting hardener ..Clive

[JAZZCNC]

I sort of made a similar frame and used epoxy like others have done on here like this:-

The bridges from one rail to the other is to allow the epoxy to self level.
The Epoxy is Wests System 205/109 very slow setting hardener ..Clive

Now I wonder who gave you that idea Clive.? . . . Lol . . . . Looking good.

[Jonathan]

Agreed with the 1600oz-in motors - they'd be excessive and might even perform worse than Nema 24 motors.


Now I wonder who gave you that idea Clive.? . . . Lol . . . . Looking good.

Me :biggrin:

[Boscoe]

Thanks for the replies guys. I'm thinking of getting frame professional fabricated because although this one is pretty good and accurate I want something getting on for perfect!


Agreed with the 1600oz-in motors - they'd be excessive and might even perform worse than Nema 24 motors.



Me :biggrin:

The motor thing is interesting, I thought they would be better especially if I used some high power drivers and high voltage rail.

[Jonathan]

The motor thing is interesting, I thought they would be better especially if I used some high power drivers and high voltage rail.

It depends, see here:

http://www.mycncuk.com/forums/faqs-problems-solutions/1524-what-size-stepper-motor-do-i-need.html

[JAZZCNC]

Agreed with the 1600oz-in motors - they'd be excessive and might even perform worse than Nema 24 motors.



Me :biggrin:

Funny that because I remember many months ago having a nice long telephone conversation with Clive about doing this.!!. .:loyal:

[Fivetide]

Boscoe a man of many talents ! Where the hell do you find the time for all this stuff lol ! looks good mate better than anything I could make.

[Boscoe]

Thanks everyone for the replies. I think I have done okay for a diy job the top rails only move out at the ends by about 1.5mm and are level within 0.2 degrees from end to end.

Unfortunately due to my limited finds going into Uni I won't be able to get the next step done for a while. I have got a few quotes on Aliexpress for the SBR20 X/Z rails and bearings - the best I got is 142USD inc postage to the UK which I think is pretty good.

[JAZZCNC]

Thanks everyone for the replies. I think I have done okay for a diy job the top rails only move out at the ends by about 1.5mm and are level within 0.2 degrees from end to end.

Maybe wrong but not sure your understanding fully what's meant with being level.? . . . Rails Being level makes no difference, they could be at 45deg and machine will still perform fine, it's the relationship between the tops of both rails. They MUST be on the same plane if not then you'll never have a accurate machine. Measuring for this is not so easy and angle doesn't come into, both rails could be perfectly level but still not on the same plane.

Has for top rails moving out 1.5mm again that doesn't matter so long has the linear rails are mounted parallel to each other.

What would matter with the top rail is if they were tilted which would make the top surface plane tilted at an angle relative to the other rail, effectively creating 2 planes at different angles to each other.
To imagine what I mean look at the top rail End on, now imagine there's a line extending parallel to the top surface or plane across to the other top rail. If either rail is tilted they won't align and you'll have 2 planes at different angles.!

Now this won't affect you to much because your planing on using round rail and the way they work it allows some error in this regards and I'm explaining this in case you win lottery or decide to blow your grant change your mind and use profiled rail also for the benefit of others who may not understand the importance.!
If you did use the much better Profiled linear rail then it would cause serious problems because when you fasten the gantry to the bearings, the bearing plates are at angle so when tightened down the gantry will try to twist them into the same plane has it and make them lock solid.

These may seem like small things but they have HUGE impact on how accurate and smooth the machine performs and sorting any error here at this stage is much much much better than trying to deal with it when machines built.!!