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DDM
08-27-2006, 09:28 PM
Well I've decided it was time to finally start on a project of my own. The machine will be a steel frame with some Aluminum parts. A working area of X-50" Y-18" and at least 12" on the Z. I will be using a linear rail system of my own design which uses skate bearings running on .875" 12L14 Hex Shafting. I plan on cutting a variety of materials from wood to some softer steels so the machine is going to have to be rigid. I have some concerns on my X axis with the placement of the linear rails. On the right view you can see how the contact angles might cause premature bearing failure and the forces for the wight and action of the Z axis will be too much for the rail and carrages running on the face of the Bridge Framework. Let me know what you think, I've still got a lot of work to do on the carrages and not much time in the shop to do them.

Carl

ZipSnipe
08-27-2006, 10:28 PM
I like it Carl! Good idea with the hex. I wonder how come no one else has thought of that? Oh well keep us posted.

mxpro32
08-28-2006, 01:48 AM
I like the hex design if you could get precision ground hex stock. is there such a thing?

DDM
08-28-2006, 02:10 AM
Ok I get in trouble about once a week at work trying to re-invent the wheel but you guys can probably all appreciate that. Here are some pics of my carrage blocks. The hex counter bored cap screw you see is the whole trick, if you leave enough space between the two sides when you put the carrage on the rail and tighten the screw down it brings all 3 sets of bearings down tight (or so I hope) on to the hex shafting making the system adjustable for wear and deformation of the hex shafting.

Thanks for the comments ZipSnipe and mxpro, we all need a little encouragement from time to time. I'm going to get screw machine stock for the hex. Most of the screw machine stock says it's good to about 2 thou but from what I've seen it's usually good through the lenght to about half a thou. Percision ground would be expensive and trying to do a 5 foot lenght on the surface grinder at work would be a pain in the @$$.

Carl

DDM
08-28-2006, 02:27 AM
Ok some more pics, I know they're just solidworks but all the same I know you guys like them. The first one is my main concern as to the location of the rails on the main bridge. I have them on the front right now in the drawing but I don't know if that with the Z axis there will be too much pull on the top rail. Tell me what you guys think. I could also position them on the top and bottom but this would make adjustment a pain because I have 10-32 cap screws going through the back of the 3 in sq tubing through a piece of 1/2 in sq stock and threaded into the hex shafting. Hope that made sense to you. Tell me what you think.

The Other pic is a rough representation of what I'm trying to build. The whole Bridge can be moved up and down for different materials from roughing out large blocks to engraving on whatever to try to make the Z travel as little as possilbe to minimize the torque on the Bridge. It can also be moved front to back to try and center the cutter to the table. So once again rip it apart and tell me to quit re-inventing the wheel :cheers:

Carl

ZipSnipe
08-28-2006, 10:13 AM
Yeah I like your carriage block design, definetly makes sense. In fact if ya don,t mind I would love to incorporate your carriage block design when I go to start my cnc project. The over all design with the overhead crane type design is one I was considering but I,m also leaning towards gantry style. But I think the double rails on the gantry is the way to go, seems like it would be more rigid.

DDM
08-28-2006, 05:54 PM
I wouldn't mind at all if you incorperated my design into your next machine. I consider most of the stuff that I do open source and I'd love to see it on some other machines. One of these days when I get some more stuff straightened out I'll post the solidworks files. I'm still concerned about the face placement of the rails and how the very top bearing is going to be pulling on the top of that rail. So if any of you engineers out there would like to share in my head ach feel free.

Carl

Dag-50
08-29-2006, 06:09 PM
Hello to all,
I see with it appeal to that been using the system from realized me for (my first cnc) in 2003, to tutt' today fnziona well and without games,
http://www.cnc-dag50.it/index.php?set_albumName=la_mia_prima_cnc&option=com_gallery&Itemid=26&include=view_album.php
Bie to all Dario
sorry for mi bad inglisc

la_coterie
09-01-2006, 02:55 PM
Yeah, I like the thinking out of the box, blue sky thinking, call it what you will.

The hex is probably a good idea and easy to fix to things. I have my doubts about the carriages, while the idea seems sound, as you say it's not doing the bearing any favours when adjusting. My thoughts are that it's over complicating the issue and requires lots of setups and acurate machining. Fine if you like that sort of thing but I'm all for the easy life :)

I always try and look at things from the mass production angle (just in case I get any ideas that might make some money :) ) i.e, the KISS principle - Keep it simple stupid (no offence intended) making as many of the bits simple and the same. Then when you discover you can't make it in your shed backtrack until it becomes possible. Often easier said than done...

Your setup is an interesting variation on a "normal" setup, You aim for a fairly rectangular machining area, I think rigidity would be increased by rotating the X axis at the top by 90 deg so the bridge has less span and therefore becoming the Y axis, this implies therefore that the moving table slideways turns 90 deg. If you were contemplating a square machining area it wouldn't make a t*ss of difference to rigidity.

I think that you are making more work for yourself by having a moving table, I believe that there would be less bits if you had all axis above a fixed table.

But hey! don't let me put you off, all thoughts/ideas are welcome here and after all it's your router - you do what you want, I'm just putting my 2 euros worth in :)

PS have you looked at my skate-o-rail, I think that would adapt very well to your hex.

Above all keep thinking out of the box, one day you'll have that idea that'll make you millions.... (can you lend me a dollar :)):cheers:

DDM
09-01-2006, 07:19 PM
Dag-50 I like the looks of your machine, It looks really professional. I looked through your pictures but I couldn't tell if you had adjustment for the bearings on your hex shaft and what kind of material you used for your hex shafting (2011, 1018, 12L14 ect). But all and all the machine looks great.

la_coterie I think you are totally right on the KISS method. This design was a lot simpiler than some of my other ideas but I think I started a loosing battle here. I've got the material cut up and squared for the carrage blocks to within -.000 to +.003 which has taken me a fair amount of time just for that stage. Plus the cost of the bar of aluminum. They wouldn't sell me just a 6 foot chuck so I had to get the whole 12 foot bar. I've got enough for two machines right now which is ok if this system works out.

I looked at your skate-o-rail and it could be adapted to my hex rails but not having a CNC to use right now would make it about as time consuming as my design considering I'll be doing this at work on an old worn out bridgeport. If they'd let me setup on one of the VMC's it would be no problem though. Now if I can just talk the boss into letting me use the swiss lathe to make my shafts. :cheers:

I thought about making this a moving gantry machine but I wanted rigid as possible and to be able to fit my size so looking at the Magazines I think the Bridge mill is still the way to go. The reason for having it so wide is that I can put a sheet of plywood or MDF on it and be able to index it across on the Y axis and for narrow material, under 12 inches wide and over 4 feet long I can index it along the X axis and not run into the posts.

Thank you to everyone for there input so far, I want to get a good game plan down before I start making everything for this machine. I'll probably do some redesigning tonight and try and get the carrage files posted on the open source.

Carl

ZipSnipe
09-01-2006, 08:30 PM
Carl don,t give up on your carriage block design. Really what it boils down to is your design requires precise alignment of the wheels to the carriage to the rail. Nothing wrong with that, challenging yes but end result is what counts. Besides if you made a carriage that was adjustable then that means you have to adjust it, and with your design no adjustment just dead on. Which is easier?

la_coterie
09-02-2006, 04:17 AM
Hmm... well you're committed I suppose, having brought the ali, I have the same problem here, I've got 8ft left of a 10ft lump of 40 x 60mm from a project. These left overs do tend to influence any future designs :)

Just make sure you build in adjustment, that way the machining doesn't have to be so accurate (so quicker) and of course all hex bar ain't the same size and it'll wear, or the bearings will.

Yes I agree that being able to move a sheet through is a good idea and the bridge idea is great, but what I'm saying is put all your movement up on the gantry. With a moving table and 8ft of sheet thats a lot of unnecessary extra weight to shunt about which will make using a vacuum table move difficult, you will need bigger motors and drives and probably increase the inaccuracy and decrease the speed you can machine large boards.

Keep us posted on them.

tivoidethuong
09-02-2006, 06:28 AM
great design

DDM
09-02-2006, 03:32 PM
Thank you everyone for their comments so far. I don't think that I was able to convey my ideas on the carrage blocks that well. They do need a fair amount of percision alingnment but there is adjustment on the design. There are two carrage blocks that in the drawing are butted up right against each other, but I have planned to have a space in between the blocks so that as the system wears/deforms you can tighten up the large capscrew on the side and pull the blocks closer together therefore bringing everything together. The shafts that run through the center work as alignment pins so that the bearings can run true to the given surface. Worst case senerio is that only 5 of the 6 bearings have contact at one time and I can live with that. I hope this cleared the air about the design. It will take some work but I'm pretty sure everything will mesh right and pull in tight against the rail. I'll try and post the solidworks files for the carrage blocks tonight if the wife will give me time.

Carl

ZipSnipe
12-27-2006, 10:46 AM
Hey Carl, Hows your progress going? I,m just getting around to implementing your ideas, however I,ve run into a problem , getting hex rod that is straight. No one sells it guaranteed to be straight. I,m waiting to hear back from Online Metals. Another problem is I keep eyeing Ebay, and have spotted some smoking deals on rails and such, but I haven,t really sat down to do a cost comparison. 2 @ 8' sections of hex is about $157 not incl. shipping. Anyway let us know of your progress.

DDM
12-31-2006, 12:30 AM
Well things have kind of went by the wayside on that machine. I was able to get some NSK LU 15 rails and trucks and am in the process of designing a new machine. As I remember I found some decent prices on www.metalmart.com for the hex rod. You should be able to go to most metal supply places and get screw machine hex stock. I was looking at some 12L14 which is a leadalloy that sounds like it machines great.

Carl