PDA

View Full Version : Problem 3' x 3' acme screw travel idea

rbs
08-12-2010, 03:46 PM
OK guys,

I'm glad that I can contribute something for once however small.

A theory really but if someone here thinks it's possible and I prove it with my build I'm working on then.. We all get a longer travel, that's if it hasn't been done already of course.

Simply, If wanting to cut with acme screws in the longer lengths on budget still trying to attain good accuracy, it's not possible over 36" due to whipping (so I've been told)Now I have a sheet piece I want to cut which is 43" tall 23" wide. All of the cutting I know will fall well with in the reachable blueprint of the the router if placed diagonally.

Diagonally on a 36x36" machine there is 50" travel so in theory could I cut my design diagonally.

I have thought it out and it seems it could work...

Even my next question, will the complexity of the design be a limiting factor and I have again come to the the conclusion that it will cut the same as if aligned normally on the X axis.

All that should need doing is to program the position of the sheet stock in CAM

What are you guys thoughts on this.?

Cheers

krak
08-12-2010, 04:19 PM
If the machine does not get interference from the stock that extends beyond the 36x36 envelope, than it should work fine. I have had two different approaches to work with pieces longer than my machine can handle. First, on a simple but large design, I split the cam into two operations. I run the first operation as normal. I flip the piece around 180 and do the second operation upside down. This works fine for long signs like " EXIT" with an Arrow.

The second idea I have had, but have yet to use is: in the design, put two holes in the stock. So my current machine has 12x12 travel, but I'm making 15x24 signs. I'll do cam in two operations again. In the first operation I'm mark two holes around 12,0 12,12. When it is time to do the second operation, I move the sign over 12 inches, and line up the router to the two holes, and adjust the offsets.

I would rather just get a bigger machine, but for now this is what I have to work with. Try it out, let me know how you do.

RomanLini
08-13-2010, 03:05 AM
...
Simply, If wanting to cut with acme screws in the longer lengths on budget still trying to attain good accuracy, it's not possible over 36" due to whipping (so I've been told)
...

What you "have been told" is not that accurate, or not for ALL cases. You can solve whipping by;
1. going slower
2. using larger diameter acme screws
3. adding some circular supports for the screws

Whipping is most likely a problem when trying to run full sheet length screws (8 foot) and with high RPM of the screw (fast travel). On a smaller machine that you are prepared to run slowish to medium speeds it probably won't be an issue.

rbs
08-13-2010, 05:59 AM
Thanks for this,

as this is my first build, I'm not sure what accuracy I'll achieve and if my piece is cut in two sections they might not line up which would spoil it's end use. But for my other projects I want to cut that concept will work so thanks again.

I'm hoping to achieve good accuracy with this altered parts list from RP to ballscrew back to Acme screws.

Cheers

rbs
08-13-2010, 06:02 AM
Thanks Roman

rbs
08-13-2010, 07:23 AM
Thanks Roman

jneutron
08-13-2010, 10:48 AM
What you "have been told" is not that accurate, or not for ALL cases. You can solve whipping by;
1. going slower
2. using larger diameter acme screws
3. adding some circular supports for the screws

Whipping is most likely a problem when trying to run full sheet length screws (8 foot) and with high RPM of the screw (fast travel). On a smaller machine that you are prepared to run slowish to medium speeds it probably won't be an issue.

Agreed. In addition, it is possible to modulate the travel speed based on the position of the axis. I've used a simple linear based velocity algorithm, peak speed being at the exact center of travel, with a linear reduction as the bearing travels closer to one end or the other.

Cheers, John

ger21
08-13-2010, 11:55 AM
What you "have been told" is not that accurate, or not for ALL cases. You can solve whipping by;
1. going slower
2. using larger diameter acme screws
3. adding some circular supports for the screws

You can also use a higher lead screw. A 5 start screw can give you 5 times the speed (ipm) at the same rpm. I have 60" 1/2-8 2 start, and I run them up to 600 rpm. They start whipping at around 400, but they're usable up to the 600 I use them at.

rbs
08-16-2010, 09:50 AM
@John, in english please. :D just kidding , I think i got that but you mean changing in mac3 or similar software right,

I have still yet to explore all the features on this.

@ Gerry

So many options, thanks for this

To be honest for this project. Speed is not important The accuracy of the objects being built.

After this machine I would like to build the ideal fast machine with better parts. I could do so now but spending the extra money on it doesn't make sense, My initial budget was just under 2000 UK and I am now trying to get it around 1000 achieving the results I need. Thanks

jneutron
08-23-2010, 11:06 AM
@John, in english please. :D just kidding , I think i got that but you mean changing in mac3 or similar software right,..

Ah, sorry.

I'm afraid that my software is not standard stuff. I run an 11 axis and a 13 axis machine which required writing my own control code. It's within that code that I was able to modulate the peak velocity based on the position of the "x" axis. I just used a linear rule calculation so that at either end of travel there was a peak speed, say 5 inches per second, and at the middle of travel, 8 ips. The code just draws a straight line between 5 and 8 and back to 5 based on where the gantry is.

Cheers, John