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  #1  
Old Sat 28 July 2012, 15:29
Dan J
Just call me: Dan
 
Florida
United States of America
Z speed - spring lag?

What kind of speeds are you folks getting with the Z? I needed to order from McMaster so I ordered the gas spring 9416K402 and it seems slow when traveling from compressed to uncompressed. I know it's recommended to not screw a nut on the bottom (piston) end but I would think that, at least occasionally, the piston rod would free itself from the bracket during rapid rises. Figured I either ordered the wrong spring or it needs "breaking - in".

Thanks,
Dan

Oh, in case anyone is wondering I went with the 50lb spring because my drop plate, router and everything will weigh about 37+ lbs. Weight-wise it's right in the middle, but I figured it would be better to have it push up than fall under a shutdown.
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  #2  
Old Sat 28 July 2012, 23:54
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Dan are you saying that you actually manage to pull the rod out of the hole? Or is that only a theory?
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  #3  
Old Sun 29 July 2012, 07:41
Dan J
Just call me: Dan
 
Florida
United States of America
No, sorry, I haven't started the build, just bought the part. It's just a theory.

I've been around a few CNC's and was hoping for a fast Z with long travel. Going from Z -15" to Z 0" would uncompress the spring and at some unknown (fast) speed it could lift the rod from the lower mounting hole. So what's that speed?

I'm just wondering how fast we'll be able to go. And, if anyone has had the misfortune of their lower rod coming out of the bracket.

Thanks,
Dan
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  #4  
Old Sun 29 July 2012, 22:26
Red_boards
Just call me: Red #91
 
Melbourne
Australia
I have a locknut holding the spring at top and bottom, but it's not wound tight and the holes are "sloppy". Having the ends held in place has helped when I dissemble the Z-axis because the spring stays attached to the spider after I remove the top bracket to free up the Z-slide (it's been easier to compress the spring and re-bolt the bracket in place than trying to compress the spring by holding its shaft).

Anyway, I have around 12" of travel and my spring is nearly neutral i.e. The router will rise very slowly if the motors are unpowered. My fast Z-moves are quite quick (300mm/s or so). No problems with spring reaction time. I rarely do a fast move from 0 to -12" :more like 0" to -3" or so. Plunge rates for me are 60mm/s.
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  #5  
Old Mon 30 July 2012, 11:41
Dan J
Just call me: Dan
 
Florida
United States of America
If my math is right, that's 660 IPM (300mm=11.8") which is great. Right where I want to be. I guess I'll go ahead and lock in the bottom (piston).

Do you have the same spring? The same weight rating or the 25lb one?

Thanks,
Dan
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  #6  
Old Mon 30 July 2012, 12:19
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Dan, realise that the "piston" is actually just a sliding block to support the end of the rod and there is a big hole through this block. Therefore, even though this spring looks like a damper, it hardly does any damping (except for a little friction). The rod, passing through the neck deal is the actual piston. The big body is just a gas reservoir. Thus, there is no delay time caused by fluid/gas flowing through an orifice.
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  #7  
Old Mon 30 July 2012, 17:10
Red_boards
Just call me: Red #91
 
Melbourne
Australia
Dan,
I had the spring custom built. I can't remember the specs, but they were close to the plan's

PS I put up a handy speed conversion table on this forum, and this shows 300mm/s ~ 709 ipm
http://www.mechmate.com/forums/showthread.php?t=3742
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