[mikeschn]

Drawer slide design...

We've got several CAD users that are willing to work on some open source designs for us. I need someone to pursue the drawer slide design. Who would like to work on that?

jpot?
chronon1?
phillby?
someone else?

Mike...

[triticale]

I'll be concentrating on this thread, but CAD is one of the things I aim to learn from this project. Right now I have some pen on graph pad sketchs exploring my angled slide notion. Should I post cleaned-up scans here, or forward to whomsoever picks up the task here?

[mikeschn]

I'll be concentrating on this thread, but CAD is one of the things I aim to learn from this project. Right now I have some pen on graph pad sketchs exploring my angled slide notion. Should I post cleaned-up scans here, or forward to whomsoever picks up the task here?

Definitely post them here... we'll look at them and try to convert them into CAD.

Mike...

[triticale]

It cleaned up fairly well. Paint Shop Pro knocked out the red graph guide lines with just a few clicks. The two lines across the top which I left freehand are the shafting for the Y axis. I designed industrial equipment for close to 20 years using pencil and paper, and changed my direction as my employer was implementing CAD.

The main premise I'm trying to raise here is the notion that angling the slides should increase stability and rigidity. With a fixed table and moving gantry, the angle would go the other way. I expect to have access to a precision cabinet shop when I'm ready to start construction, but consistant angled wedges could be cut with a miter saw.

[ger21]

You'd be better off using 2 pairs of slides at 90° to each other. With your method you will still get a little play in the movement.

[triticale]

Originally posted by GER21
You'd be better off using 2 pairs of slides at 90° to each other. With your method you will still get a little play in the movement.

Believe me, if there'd been two pair in that dumpster I'd have grabbed them both.

We know that one pair of good slides, installed in the standard manner, does a minimally sufficient job. If my idea is valid, it would cut the investment, for anyone shopping from the plans, in half while still yielding some improvement. McMaster (never the lowest price, but cheaper for industry than chasing down the deal) wants $64 a pair for their closest equivalent.

[fyffe555]

I'm with Ger on this one.

Draw slides take loads in one plane only. Sit at your desk and half open a draw, lift it up and down and it shouldn't move, move it side to side and it will move a long way, wrack it diagonally and it will move about the same.

A gantry cnc will load its bearings in two dimensions and try to wrack the gantry in the same way as the draw test above. Add the leverage and distance of the cutter from the bearing and you've got problems.

I don't know what brand the slides are that were proposed for a diagonal mount but I've got some Home depot full extension high capacity slides here and trying it (before posting) they bind quite badly on a 45%.

Reading this post and the other recent posts about the new designs it strikes me there's little talk of the loads the machines have to be built for and how the different materials and bearings will need different design points in the construction of the machine.

For example given the draw slide option and the loads a cnc machine imposes the slides has to suport two planes of load and so in the ideal solution you'd need two sets one 90% to the other as Ger suggested.

Similarly the black iron pipe skate bearing arrangement has limits and challenges on the span a pipe of a given size can support, the need for support and the need for adjustment. It's not practical to significantly increase the dimensions of the JGRO router and expect it not to deflect big time.

In the same vein a lot of the gantry designs have simple uprights and back plates with no triangulation or support while the tube/rod is supported at the ends only by the thickness of MDF or the ends of bolt heads. They need way more support than that.

Some thought needs to go into the manufacture of the parts for alignment too. Since most of us ( except Ger apparently ! ) can't get our parts cut on a cnc machine first, then the design should avoid excessive number of joins or hole alignments, use techniques like cutting parallel dado's in one go on one board and then cutting the parts from that, bolting together enda and bdrilling all as one part to approximately line up holes, that sort of stuff.

It strikes me that there's a lot of enthusiasm ( which is great) to develop the machines but the engineering of each option has yet to catch up.

Andrew

[vladdy]

Is this the kind of critter you are looking for??
don't have any cad [or any other, for that matter] drawing for, pretty simple to put together..
a good square, tape measure, and a saw..

[mikeschn]

It strikes me that there's a lot of enthusiasm ( which is great) to develop the machines but the engineering of each option has yet to catch up.

Andrew

Do we have any engineering types here? Or are we all machinists and cad users?

Mike...

[mikeschn]

Okay, let me just throw out a quick idea for the drawer slide design...

Both x and y have the drawer slides mounted at 90* to each other to keep things from shifting.

This is really going to be a simple thing. The table moves, and the gantry is fixed.

Is this the direction we should be taking?

Mike...

P.S. Are drawer slides in Europe metric? Can someone point me to a URL for metric drawer glides?

[Evodyne]

Okay, let me just throw out a quick idea for the drawer slide design...Is this the direction we should be taking?

Mike...

Mike,

Hi. My concern would be that the width of the table might work against you-see the attached pic. What about using the slides as they would normally be and use another method to limit movement in the unwanted directions? Something like delrin guides to contain the slop?

Lance

[jerber]

Okay, let me just throw out a quick idea for the drawer slide design...

....

Is this the direction we should be taking?

Mike...

P.S. Are drawer slides in Europe metric? Can someone point me to a URL for metric drawer glides?

As far as I know they are metric, but only on this side of the tunnel.

http://www.chambrelan.fr/en/pages/interface/iframe.htm

or www.chambrelan.com with intro.

Is it an idea to use more then two slides per axis ?
It's harder to line them out and there will be more friction but "accuracy" and the load will inprove.

[fyffe555]

Do we have any engineering types here? Or are we all machinists and cad users?

Mike...

There are a few, but then the engineering understanding necessary to be a machinist or professional Cad should be enough.

Your idea of using two slides at 90; draw slides support in one plane and allow movement in the other, so in your diagram the left hand slide would locate in the horizontal and allow some movement in the vertical. The right hand slide would locate in the vertical and allow movement in the horizontal. Together they could allow a rotation about the right hand slide. In other words the left hand side of the upper part could move up and down.

An alternative would be to put two slides at either end and another in the centre at 90%. Depending which way you orient them they will should locate the top part in both planes and have greatest capacity in the plane common to the two end slides...

Or put two at 90% at either end.

All three examples could work - it depends on what loads and their directions your machine produces, and your target precision might be.

[mikeschn]

Draw slides take loads in one plane only. Sit at your desk and half open a draw, lift it up and down and it shouldn't move, move it side to side and it will move a long way, wrack it diagonally and it will move about the same.

A gantry cnc will load its bearings in two dimensions and try to wrack the gantry in the same way as the draw test above. Add the leverage and distance of the cutter from the bearing and you've got problems.

Andrew,

I'm counting on you for a little bit of the engineering help. Is that okay with you?

Mike...

P.S. On the drawer slide design, is this what you were suggesting?

[turtlekilroy]

I'm new here and have been following the DIY posts with some interest since I'd like to put together a small CNC router to mill out PC boards at home. I liked the idea of using drawer slides but it seems to me that the table might tend to sag a bit at full extension even with full extension slides.

The simplest solution I can think of is to use 2 sets of full extension drawer slides on either side positioned so that when one is at full extension the other is and minimum extension in order to more evenly support the table. The only thing is that this approach might make it more difficult to mount.

[mikeschn]

The more I look at drawer slides, the more difficult it gets to come up with something that has any reasonable amount of precision.

I'm starting to think that the approach we should use is just build a cnc mill with 3 slides on the x axis and y axis, and accept the inherent play in the system. Like this pic...

How do we do the z on this system?

Mike...

[pminmo]

Maybe add some roller bearings to help take up the play?

[ger21]

If you want something to work pretty well with drawer slides, You need to use 2 pair per axis. 1 pair at each end opening towards each other. The reason is, the farther you pull out a drawer slide, the weaker it becomes. By putting them opposite each other, one pair will be in the closed position when the other is fully open, so you should get fairly consistent operation that way.

A good place to get slides at decent prices is http://www.wwhardware.com
I'd recommend the Accuride 8400 series. Probably the best deal for the money. When you go anything heavier duty the price starts to go up fast.

[Craft Worx]

Hey All,

I have been lurking around this forum for about a year or more, and have realy been interested in the drawer slide idea. I have a furniture building background so I have a lot of first hand knowledge of the guides.

I have seen you guys talking about the different brands out there and the differences among them. It have found that almost all of them are Accuride copies.

I found a Liberty brand guide at my local Home Depot (Dallas Texas). 16 inches, full extention, ball bearings, etc. $16 a pair aint nothin to wright home about, but it beats some of the other prices I have around here with a stick.

I am currently working on modifying one to work more like a pocket door slider, where it can travel past closed. This will keep the load bearing portion inside the base part of the guide, keeping its rigidity.

I am taking pictures of what I am doing and will post them when I have a sec.

All of the work will be done with a dremel, drill press (hand drill will work) and pop rivets. So the average Joe should be able to pull this one off with ease. I will make a tutorial if I get enough requests.

Keep Up The Constant Thinking,
Aaron

[lucas]

The more I look at drawer slides, the more difficult it gets to come up with something that has any reasonable amount of precision.

I'm starting to think that the approach we should use is just build a cnc mill with 3 slides on the x axis and y axis, and accept the inherent play in the system. Like this pic...

How do we do the z on this system?

Mike...

Mike,

this should work, but:
I want the drivenut in the exact center between the rails, if you put it too much on one side it will create twist and friction in the table. If the table is wide enough then the center rail and nut can be as close to the center as possible.
Ger21's solution is better but needs an extra rail.

I have rebuild my second machine using modified drawers (I think the same way Craft Worx does).
This is it:
http://users.skynet.be/sky50985/CNC/Xaxis1.dxf

I only have the 2 slides now and it looks stable, real tests will show if it's good enough.
Assembling like this is simple, just drilling holes and some bolts and screws.
The U shape will also hold the fixed sides for the Y
This is for a small machine mainly for pcb drilling and milling soft materials.
The drill/router will be 50 or 160W max.

The Z can also be done with drawer slides, disadvantage is that you need a rather long rail for stability resulting in a tall system, and again 4 pieces..........
I made my Z like this:
http://users.skynet.be/sky50985/CNC/Z_axis_concept.dxf

There are 2 things wich could be improved or changed for ease of construction.
1: I drilled holes in the guide bars, taped them and used screws to fix them between the top and bottom plate, can't do this precise so I had to use oversized holes for adjustment. I think it will work for me but for a 1HP router?
2: the bearing in the bottom has to absorb all up-downward forces. again I used a light construction and hope it will hold.

Another problem could be the nylon or teflon for the guides and nut.
I was lucky to find some leftovers but don't know if you can easily buy this.

Idea's for improving these?

Will try to post some pictures when it's reassembled, all 3 axis are finished, steppers are mounted and all seems fine.
I used standard M10 threaded rod and can run higher than 2500 mm/min (100IPM) with small steppers from a matrix printer (5V 0.8A).


PS: Do these DXF's create a problem or does anybody knows a good (0$) way to convert DXF to JPG?