Steel Framed Router

[GTJim]

Hello. I am hoping to design and make a router for hobby use just like many have done previously on this site, and I am currently putting together a concept and these are my current thoughts.
I am aiming for a working area of 1000mm x 1300mm (approx 3’x4’) and a Z of 130mm (5’’).
The main frame and gantry is currently 50x50x4 steel square hollow section with 25x25x2.5 bracing for the bed. This will be bolted together unless I find a good welder.



The linear rails are 25mm dia for the Y axis and 20mm for the X and Z, and hoping to use a 2510 ballscrew for the Y a 1610 ballscrew for the X and 1404 ballscrew for the Z. (hope I haven’t confused the X and Y).





I would appreciate your comments and constructive criticism as the design is easily changed at this stage before any serious money is spent. This is only a hobby machine and its main use will be engraving hard wood panels and cutting out the odd speaker panel.

[luke11cnc]

hello first

If you are using 25mm supported rails you will need box of 60mm and over

plus two ballscrews as to stop the bed crabbing

this is just the advice I have received as I'm by no means a expert

you may want to look at Jonathan's and chips CNC machine
James and Luke

[GTJim]

If you are using 25mm supported rails you will need box of 60mm and over
plus two ballscrews as to stop the bed crabbing
James and Luke

Hi Luke,
I have details of a fully supported rail that has a 21mm dimension across the base. I hope it is still available.
As for the crabbing, I was hoping by spreading the lower bearings apart as far as I did this may be avoided, but I will take the comment on board.

Jim

[Ricardoco]

Hello. I am hoping to design and make a router for hobby use just like many have done previously on this site, and I am currently putting together a concept and these are my current thoughts.
I am aiming for a working area of 1000mm x 1300mm (approx 3’x4’) and a Z of 130mm (5’’).
The main frame and gantry is currently 50x50x4 steel square hollow section with 25x25x2.5 bracing for the bed. This will be bolted together unless I find a good welder.



The linear rails are 25mm dia for the Y axis and 20mm for the X and Z, and hoping to use a 2510 ballscrew for the Y a 1610 ballscrew for the X and 1404 ballscrew for the Z. (hope I haven’t confused the X and Y).





I would appreciate your comments and constructive criticism as the design is easily changed at this stage before any serious money is spent. This is only a hobby machine and its main use will be engraving hard wood panels and cutting out the odd speaker panel.

Hi Luke,
I have details of a fully supported rail that has a 21mm dimension across the base. I hope it is still available.
As for the crabbing, I was hoping by spreading the lower bearings apart as far as I did this may be avoided, but I will take the comment on board.

Jim

Hi Jim, the design looks cool, I notice that the side bracing for the gantry is biased towards the spindle side of the gantry is this by design, IE is the Z axis and spindle going to exert a greater downwood force than the upward force generated while cutting.

Ive seen the crabbing or twisting of the gantry avoided by framework being added to the opposite side of the gantry to the spindle as in the commercial machines.

These are just observations and are not supposed to imply any knowledge or special wisdom on my part.

Oh and what software did you used to produce the pictures?

Rick

[GTJim]

I notice that the side bracing for the gantry is biased towards the spindle side of the gantry is this by design, IE is the Z axis and spindle going to exert a greater downwood force than the upward force generated while cutting.

Ive seen the crabbing or twisting of the gantry avoided by framework being added to the opposite side of the gantry to the spindle as in the commercial machines.

Oh and what software did you used to produce the pictures?

Rick

Rick, I am unsure about cutting forces but I was hoping to prevent the gantry flexing back and forth while cutting. I may also add a plate to the back of the gantry between the X axis to further restrict right or left deflection.
I just used Google SketchUp for the drawings as its quick.

Jim

[Ricardoco]

Rick, I am unsure about cutting forces but I was hoping to prevent the gantry flexing back and forth while cutting. I may also add a plate to the back of the gantry between the X axis to further restrict right or left deflection.
I just used Google SketchUp for the drawings as its quick.

Jim

I know its cheeky but can you send me an editable version of drawing two and i can modify it to show you what i mean..

[Jonathan]

The plate on the gantry to stiffen it is an excellent plan. I think you need to consider more how you are joining the box section, and gantry sides to bearings. Currently you have drawn the box section attached on just one face which is a bit weak.

I have done a drawing for you to illustrate how I think it can be made stronger:




That way the sheet reinforces the joints in addition to the general structure. I would be inclined to weld it for good measure. If not put plates (say 20mm thick) in the ends of the box section and bolt into them.

[JAZZCNC]

The linear rails are 25mm dia for the Y axis and 20mm for the X and Z, and hoping to use a 2510 ballscrew for the Y a 1610 ballscrew for the X and 1404 ballscrew for the Z. (hope I haven’t confused the X and Y).

If these are profiled linear rails you dont need 25mm they will be massively over kill. 20mm will be more than enough, even 15mm will be good enough. I'm talking profiled linear thou not round supported.

25mm ballscrew is also not recommended for a machine this size, you've probably gone with 25mm because of the 10mm pitch not being available in 20mm.
25mm screws are large and they produce a lot more inertia which has to be stopped and accelerated this means big strong motors needed amongst over things which all make it not ideal.! . . . Bigger is not better when it comes to some things, screws being one of them.!
At the size your looking to make 16mm is getting on the edge of being whippy thou with carefull aliagnment and sensible speeds you would be ok.
You could go with 20mm 5mm pitch and gearing 1/2 this way you get the speed thou at the cost of a little torque. I can tell you from experience 6nm Nema 34's will handle 1/2 setup without any problem. There is an up side with 1/2 gearing as well to this if you find you ever need the extra resolution of 5mm pitch and higher torque it's a simple pulley change and away you go.

You could go with rotating the nut but it gets a bit more involved, thou does work well if done right.

With the steel box section frame you will also get lots of resonance which has a big affect on quality of cut esp when cutting hard materials so a big tip if you go all steel is cap the ends and fill the frame with kiln dry'd sand it makes a big difference.

Definatly go with twin screws on the X axis it makes a very accurate strong stiff machine. Either with a motor on each screw slaved together or one motor with belt between the 2 screws.
Dont be put off by the belts they work fine and more than good enough for the work you intend to do. I have a machine that use's this 5mm pitch 1/2 twin screw belt setup and I cut every thing from steel to plastic with it no problems and it's super accurate. Even cut cast iron with it last week for the first time without any trouble.!
Not a pritty thing but it gets the job done and very very reliable and super accurate.

Cheers.

[Jonathan]

25mm ballscrew is also not recommended for a machine this size, you've probably gone with 25mm because of the 10mm pitch not being available in 20mm.

Maybe 16mm screws with 10mm pitch - RM1610.

25mm screws are large and they produce a lot more inertia which has to be stopped and accelerated this means big strong motors needed amongst over things which all make it not ideal.!

I was about to suggest looking into using rotating ballnuts...

You could go with rotating the nut but it gets a bit more involved, thou does work well if done right.

But you beat me to it! You might be interested in how I did the rotating ballnuts on my machine:

http://www.mycncuk.com/forums/showth...t-design-ideas

They work well, so I guess I did it right.

I agree with using belts and two ballscrews on the X-axis. Spacing the bearings further apart will help prevent the gantry racking a bit, however it's still not ideal.

i wouldnt look at my build for any design inspiration,its a bad build and a lot of good materials wasted,im on the verge of scapping most of it and starting again:tup:,

Oh don't say that ... you're doing yourself a disservice. There's still room for improvement on mine and there always will be. The distance parallel to the X-axis from the Y ballscrew and cutter is far too great on my machine for instance.

[GTJim]

I've just started looking into the possibilities for pulleys for the ball screws and stepper motors.

I understand HTD belts have been recommended, but my problem concerns the spindle on the motor I'm considering, it's Dia 8mm x 21mm long approx. I don’t really want to use a belt less than 15mm wide but can't find a pulley to fit the length of the motor shaft.

What has been used before, any ideas?