Air cutting & shuddering

[dubliner]

I was air cutting and I noticed when I cut an arch of 108"x & 28"y with a speed of 11.5 IPS at the same 2 points on the arch apx half way out on the Y & half way back. It was fine at 11 or below. It sounded like the pinions were binding against the rails but there was none that I could see but I could hear & feel it. BTW I could not replicate the noise or shuddering with straight moves on X or Y with faster speeds than 12IPS to the same destinations . Was I pushing it too fast on a compound cut?

[scottcox]

Neville,

There are some threads here on the forum that discuss the harmonics of the machine causing vibration in exactly the manner you describe.

You may want to try searching out past discussions for info on that.

Scott

[dubliner]

Yes I searched but the only pertinent discussion was on Wes Mason's PRS so I dont think I can use all the other (PRT's)data for a fair comparison, perhaps I can?? I'm wondering if anyone with a PRS alpha had the same issue exhibit itself at the same speeds? Would I ever be cutting anything at 11.5" IPS or above anyway?

[dirk]

Sounds like a comunication bottleneck. Check your thouroughput speed with the diagnostics tool. Using an inexpensive USB 2.0 hub between your computer and tool will usually speed things up.
Dirk
Check Brady's post concerning this issue.
www.talkshopbot.com/forum/messages/312/21937.html#POST53253

[dubliner]

I tried adjusting the ramp values but experienced the same problem, then I ran the comm. test and am getting 73.9% So I guess I will try a hub, I could use an extra few feet of cable anyway. Interestingly it happens at 11.7 IPS but not at 11.6. Thanks for the advice - Nev

[dubliner]

FYI - Installed a 7 port hub from Radio Shack $14.95, went up to 85% comm rate & got rid of shudder at 12IPS. If you go to RS, their 4 port hub was $40, but the 7 was on sale - Thanks Dirk - seems like that was the solution.

[jay_p]

Dirk,
Are you suggesting a powered hub (with external power) here, or just a simple hub? And which did you by Neville?

Jay

[Brady Watson]

As posted by Dirk: Read This Thread (http://www.talkshopbot.com/forum/messages/312/21937.html#POST53253)

The 7.2:1 motors turn 7.2 times faster than the 1:1 motors (on paper) and as a result require better communication in the upper end of their speed range.

-B

[dirk]

I've bought some hubs at Walmart. I usually buy one that is compact for a note book that is self powered. Basicly by using a true 2.0 device it forces your computer to configure it's resourses for 2.0 at that port. The Aten USB to Serial adapter is not a true 2.0 device, so the hub solves the bottleneck at the computer.
Dirk

[jay_p]

Sorry Brady, missed the link. Thanks for the info all.

Jay

[dubliner]

Just as you advised in the thread Brady, it fixed the problem thanks. The hub I bought was Gigware? I think. Its in the workshop & I'm not, but if you need to know I can look.