Re: [CAD_CAM_EDM_DRO] Re: Acceleration rates..

Jarrett,
Most people adjust speed and accelleration by trial and error.
Use a low accelleration at first that you're sure won't stall the motors, then keep raising your max speed until it stalls, then
back off 20% or so.
Then set your acceleration the same way, by raising the values until it stalls and then back off.
There is a lot of difference in the way a large router will be set up vs. a small mill IMO.
I found that I had to back off the acceleration on my router to way below the maximum values as the start and stops were way too
rough.
BTW I built my router for a similar purpose. it's 4'x13'x12" and will be using it cutting foam molds for concrete. Could you
elaborate on the "spray on bondo" as I haven't yet found anything to build up the surface a lot that doesn't eat the styro.
Thanks,
Brad

----- Original Message -----
From: "Heidi Johnson" <hjjohnson@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: November 25, 2005 8:02 AM
Subject: Re: [CAD_CAM_EDM_DRO] Re: Acceleration rates..


> Les Thanks for taking to time to reply.. I'm sure its evident that I'm a newbie when It comes to machining and machine work. My
primary objective w/ this system is to make composite molds by first machining mid density foam in a rough cut form, then coating
the mold with several coats of high build primer [ spray on bondo] and then re-machining to a decent finish which will then be just
touched up by hand sanding w/ a sanding sponge to take out any ridges.. spray with a tooling gel coat and pull my mold from this..
Almost all of the parts will be 3D. The system I've 'proposed' is fairly large, approx 16'x 10' x 5' in size.. this is still
changing a bit but.. thats close for a ruff idea. I was thinking that acceleration rates would be key in this regard.. and this is
why I was asking.. I'm also struggling in calculating them out.. so.. At this point I'm not even sure I have it right. One of the
fellows off Cnczone thinks I'll have 0-400 ipm in 0.06 seconds.. This is based on
> 900 oz force and a 200lb gantry.. I didn't get this number when I calculated it.. however I'll wait until he clarify's his
numbers so I can understand how he's calculating this. And as an aside note, it will actually be 1800 oz force as I'm doing some
gearing in there to get better torque... which if his calculations are correct means 0-400ipm in 0.031 sec. I think that could be
sufficent however.. I'm not convinced this is correct as of yet.. [ I'm still hoping it is!!]
>
> Jarrett
>
> ----- Original Message -----
> From: Les Newell <lesnewell@...>
> Date: Friday, November 25, 2005 4:29 am
> Subject: Re: [CAD_CAM_EDM_DRO] Re: Acceleration rates..
>
> > Hi Jarrett,
> >
> > Acceleration is often more important than top speed. What is the
> > use of
> > a machine capable of 400IPM if it needs half of it's travel to get
> > up to
> > that speed? Twice the acceleration and half the top speed would
> > end up
> > being quicker overall. What sort of work are you intending to do?
> > If it
> > involves lots of long straight cuts then acceleration is not all
> > that
> > important. If you are cutting a lot of detail then acceleration is
> > vital.
> > I would say that in general you don't want the machine to take
> > more than
> > 0.5 second to get up to cutting speed. Remember when you go round
> > a 90
> > degree corner one axis has to stop and the other axis has to
> > accelerate
> > to speed. If you have low acceleration then the machine is going
> > to
> > crawl if it needs to cut a complicated shape. Get hold of a copy
> > of
> > Mach2 or TurboCNC and set it up with your expected acceleration
> > and top
> > speed parameters. Now run a job and see what speed the machine
> > actually
> > runs at. You will then be able to play with the values to see what
> > effect they have on the overall cut time.
> >
> > Les
> >
> > Jarrett & Heidi Johnson wrote:
> >
> > >I'm working through some design disicions and trying to get my
> > head around
> > >mill acceleration. My plan is to mill foam predominantly. I'm
> > wondering if
> > >acceleration rates are really a concern or not. I would figure
> > that not to
> > >many people want there system to take 5 seconds from a stand
> > still to
> > >accelerate to 10 ipm or something but.. what is acceptable? I
> > would like to
> > >rapid @ ~400IPM and be able to accuratly mill at up to 200-
> > 250IPM. The
> > >system I'm looking to build has a fairly large foot print with a
> > ~200lb
> > >gantry. Obviously 120 oz-in steppers won't cut it [ pun intended]
> > but..
> > >should I be able to go from 0 to 250 ipm in 5 seconds?
> > >Does it really MATTER? Am I looking at the wrong side of the
> > design??>
> > >Opinions welcome!!!
> > >
> > >Jarrett Johnson
> > >
> > >
> >
> >
> >
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> OFF Topic POSTS: General Machining
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you have trouble.
> http://www.metalworking.com/news_servers.html
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> http://groups.yahoo.com/group/jobshophomeshop I consider this to be a sister site to the CCED group, as many of the same members
are there, for OT subjects, that are not allowed on the CCED list.
>
> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO
EXCEPTIONS........
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