[High Seas]

piminmo -
Phil and all participating - I really like the way this is comming together. Been "off" for the weekend and you've created a "model" of the communicarioni process I think we'll be useing for the DIY CNC IPT "thing"

You're all invited to volunteer to join there too. Great work guys!
cheers - Jim

[pminmo]

Damachine I like the idea! Meets the KISS test!

Something I'm finding myself debating is cheap, simple and fast vs. a few dollars more, more work and maybe higher accuracy. For example a good pair of drawer slides for an axis vs. drill rod or cold rolled and a truck assembly. Take a Y-axis:
Two flat surfaces two drawer slides and you have a functional moving axis. Cost of the rails maybe less than $30. Maximum travel probably 26".

To accomplish the same with rod, you have to add two or more truck assemblies, holding methods for the rod and a more difficult alignment at minimum. Drill Rod approximately $30, truck assembly $? The benefit (possibly) would be more precision and repeatability.


Food for thought.

Question for the interested parties, how long do we want to brainstorm before trying to zero in on some specifics? Would there be any interest in a net meeting via a chat room setup?

Phil

[pminmo]

Vacpress, keep the rambling going, I like it.

Phil

[Ferenczyg]

I always thought that drawer slides, at least the ones I know, will limit the workable area, or if we want to take profit of all the displacement, will increase the footprint of the machine. If you permit some bad ascii art to explain myself, one rolled slide is like this:

=============
############
=============
<------- L ------>

an 'unrolled' or 'unfolded' drawer slide is like this (ignore the · characters plz):

==============
················############
························· ·····==============
<-------- D---------><-------L-------->

I got some questions about that:

1) The overhang D will protrude from the sides of the machine increasing footprint artificially from L to 2D+L being D always unsupported.

2) If we limit the overhang from D to the expected footprint, we are loosing working area

Do you know some tactic to avoid these issues? I am not saying that drawer slides are a bad idea, in fact i think is the paradigm of KISS, but do you think there is a solution for the problem or is something we must 'live with it'?

Thanks in advance

Fer

[pminmo]

The overhang could be supported by bearings, furniture glides. You will almost always lose some usable travel regardless of method. i.e. a rod and bearing will lose the width of the spacing between the bearings.

Anybody here good with 3D cad?

Phil

[Ferenczyg]

Originally posted by pminmo

Anybody here good with 3D cad?

Phil

Vacpress.. someone is calling you

[vacpress]

what cad stuff is needed? i think it will be a bit till designing really starts on this - when it does, i intend to make the final materials very nice looking - regardless of who designs it and what it really looks like.. i also will build along at least 1 machine, to act as a beta tester.

for now, sidelines... got final exams comming up also.. 5 weeks..


i do have some drawer slides around - maybe i will do em up in 3d to get ready...

thats another idea - it seems like lots of users here have allready drawn up alot of the parts we may use - i know i have drawn dozens of bearings, motors, extrusions, etc.. maybe we need a central database of 3D files?

i love solidworks, and think that would be a way to go.. not cheap at all though...

www.3dcontentcentral.com is a site that may serve as a model for a 3d data repository - mayeb whatever project management software CNCadmin endsup with will have provisions for this?

[sol]

I have tried drawer slides and have been very disappointed with the results...I used the best slides that Lowes offered too, but that does not necessarily mean much. There was a lot of wasted length and floor-space as Fer mentioned, and there also was a lot of play in every direction.

As for trucks that do not require welding or casting: Here is a link to a detail I wrote up last fall...Personally I would (and have) used them instead of drawer slides.

I am not trying to push an agenda here, just thought I'd share what I learned the hard way.
http://solsylva.com/cnc/cnc5.html

[Rhodan]

Originally posted by pminmo

A lot of noise potential.

Yeah, I've had some experience with compensating for noise - analog sensors for temp, pH, ORP, etc. Have my O-Scope ready for the first PCB (I make my own).

#2, using mechanical relay's to switch inductive motor loads is a second noise generator. Physical layout will be of utmost importance.

Just received some IRL520s on Friday. Going to replace the VBB relay with one of these. 100V 9.2A Hexfet. Fully on with only 2.5V at the gate 8). Digikey has them pretty cheap too. I'll probably add EStop to the auxiliaries now, didn't before mostly due to cost and board space when dealing with relays.

I went with a single channel design for a couple of reasons.

Actually, I was mulling that idea around too. Use four boards, three identical driver boards and one breakout/switch board. Not so much for noise as for ease of PCB construction/replacement. My first prototype was going to be a single channel with the breakout/switches anyway just for testing.

One specific suggestion, seperate Vbb1 and Vbb2 with a 100uf cap close to each pin on the 3977, for an additional 25 cent component for each axsis, its good insurance. If I can be of any assistance write.

Phil

I was going to see how that performed on a PCB. I was originally thinking of tossing a much larger cap there to cut down on the current pulses through the 24V Trace. Thats where most of my noise concern is.

[Rhodan]

Originally posted by sol
I am not trying to push an agenda here, just thought I'd share what I learned the hard way.
http://solsylva.com/cnc/cnc5.html

I'm with you Sol, my first machine is going to be a "throwaway". Its purpose is to teach me, not actually be a truly useful device. Though if I'm really lucky, perhaps it'll be both

I actually think that might be a good plan for this project. One dirt cheap plan for first time builders that is meant as a tutorial, then a second plan that is actually meant to be a useful machine.

[pminmo]

The reason I asked about 3D capability was to concept ideas for details. i.e. bearing blocks, gantry, portion of assemblies....

Things to ponder:
1. What is reasonable to expect regarding tools required?
2. 3' or under on the longest axis ok?
3. Does it make sense to work in assemblies, with a goal that the assembly interface is compatable with a cheaper or more accurate version?
4. Does it make sense to focus on X axsis to start with?

Phil

[sol]

Thoughts on the above questions:
1. Tools required? A hand saw and drill... so that the project can be made by an apartment dweller on his patio, or a kid in his back yard and bed room. Major cuts in the MDF could be done at the lumber yard, first few are usually free and then they are just 25 cents each or so; this also makes it far easier to lug the MDF home. An entry level Proof of Concept router should be build-able by anyone anywhere.
2. Three feet or less is fine. Lumber yard threaded rod comes in 3 ft lengths (USA, duh )
3. Maybe... I can argue that one either way. Once a person has built a router with plans as a reference wouldn't he be able to take the next steps on his own from there?
Switch out what? Gas pipe to drill rod to Thompson rails; lumber yard threaded rod to ACME to ball-screw thread... is there any point in upgrading to high end components on a chassis made of MDF?
I would focus on making each component simple and cheap so that it is obvious to the builder that the concepts are scalable.
4. Gotta start somewhere and since the works sit on X and X is usually the longest axis why not?
Make it just enough under 3 ft. so that an uncut threaded rod will protrude out an end of the frame far enough to connect to a motor. To make X, length of Y has to be known as well...what do y'all think would be a good width?

My free advice and worth what ya paid for it.

[Hobbiest]

I don't know why everybody is so concerned with using off the shelf length all thread. A hacksaw cuts it in no time, and a dremel with an abrasive wheel is even faster. I agree with some of what is being said. I think that the focus should be an entry level, "so those are all of the parts that make one of these things" machine, as well as teaching the relationship of the components. Once somebody has built a machine, it is usually much easier to design/build the second one.

[pminmo]

For discussion, end view. 3/4" base (crosshatched), Gantry (red)1 1/4" drill rod, a bearing assembly out of Acetel (delrin). There are three elements to the picture, two virtually identical end views, and a smaller drawing at the bottom of a bearing assy. Delrin is easy to machine, fairly slick. Widely available online, McmasterCarr, ENCO, Ebay. The bearing would be made out of 1.5" x 3/4" rectangle, bolted together or clamped. 1 1/4" hole drilled at junction of the two halves of delrin. Most moving gantries show two equal slide mechanisms. Why? A bearing that is captive 180 degree's holds two axis fixed. The second side would only need to hold the Z direction captive, then parallelism between each linear rod is not as critical. Second question, why have the rail at the extreme's of the axis? Compare the two end views. If the left rod is moved towards center several things happen. 1) Load from the cutter pushing down over the rod is more evenly distributed. 2) play between the bearing is less amplified at the other end of the gantry. Thought, for X why not put a little more effort into one linear ways?

Phil

[Damachine]

I would like to second Rhodan's motion.
A fairly "simple" inexpensive machine that is reasonable for first time builders and an education for the team that builds it.

The plans for a basic machine could be written in a step by step format. You know, "Follow the instructions and you end up with a working machine" kind of instructions.

After the team and community have gotten up to speed a second modular machine could be designed. With more general guide lines instead of instructions. Maybe break up that design into sections. Tables with 2 or 3 designs, another section with different type of boards and so on.

I would rather we don't design a "throwaway" machine even if it is educational. We should be able to design a "small" (small usually cuts cost and complexity) decently accurate machine., that should be able to do decent job on small parts.

[chuckknigh]

I was in Home Depot, and got looking around. Several people were concerned about using gas pipe for rails, since it would infringe on JCK's idea, even though it is clearly public domain.

There is another choice of easily available, stiff pipe at Home Depot. Chain link fencing top rails (small) and posts (big) for rails. EMT is another good choice, but it's more expensive.

Using such commonly available components (is chain link fencing available in Europe?) would be a very good idea, and further reduce costs.

I'm hoping, personally, that a machine could be a viable science fair project for a teenager. That seems like a good goal.

-- Chuck Knight

[Ferenczyg]

Chuck, what is 'chain link fencing'? I'm in Europe but the name does not have any meaning for me.. maybe is my level of english but I hate when I go to the hardware store and say 'have you got..' and the only response is a weird face..

Thanks in advance

Fer

[pminmo]

Chuck, A science fair project would be a good objective. Might be a challenge to the normal kid, but we've probably all seen some of those science fair projects that totally blow a person away. I personally don't have a problem with using gas pipe, while cranky may be the most recognized for it, I don't believe there are any intellectual property issues.

Phil

[pminmo]

I arbitrarily set a target of $100 for the mechanicals less motors and electronics. All the objectives are modifiable at this point, lets shoot for May 1st as a point to firm up the objectives. By firming a set of objectives, we can limit design goals to what fits the objectives only.

Phil

[ToyMaker]

Chain link fencing posts and rails, and emt are galvanized. Almost any kind of wear on the surface will cause galling and flaking. The reason for using gas pipe (also called black pipe) is that it is not galvanized.

robotic regards,

Tom
= = = = =
It is a thousand times better to have common sense without an education than to have an education without common sense.
- - Robert G. Ingersoll