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View Full Version : which size is better alround



deannos
08-01-2012, 12:06 PM
While i'm gathering parts for a new build, i want to use the full 48" on my current "MDF" build. I have been looking at MD on *bay and these 2 sizes, it will be for my x axis

TR16x4D

TR12x6-P3D (2 start)



Jonathan if you read this will your bearing thingy majig work ok on any of these. I'm currently using it on the x with the 16x2 you sold me and it works ok, don't fully understand how it actually works but it does. Would you be able to make a couple of nuts for either of those rods if the bearing does

Jonathan
08-01-2012, 12:54 PM
The TR16x4D moves 4mm per revolution, and the TR12x6-P3D moves 6mm per revolution. Comparing the critical speed of the screws, which is the speed at which the screw starts whipping, for 48" long the 16x4 gets 3090mm/min and the TR12 is 3430mm/min. That implies the TR12 will get a higher feedrate, but the difference is very slight. Bear in mind the formula for critical speed from experience gives an underestimate.

The other consideration is the power required to accelerate the screw. For the TR12x6 it's much less as the diameter is less and the pitch is greater. If you're not using pulleys I'd go for the 12mm, with pulleys then I'm not sure really ... there's not much in it.

Actually that's not true - I replaced it with a RM1610 ballscrew from Chai:

http://stores.ebay.co.uk/linearmotionbearings?_trksid=p4340.l2563

It's about 70 including postage for one 1200mm long ballscrew with the ends machined and a nut. About 32 for the trapezoidal screw as you already have the 'nut'. The efficiency of a normal trapezoidal screw/nut is less than half of that of a ballscrew which is why I made the rolling nut as that, like a ballscrew, uses rolling friction.

The bearing nut thingy (picture below so everyone else knows what we're talking about!) should work better on a trapezoidal screw than the M16x2 threaded rod you're currently using. Just need to make sure it's the right size to engage properly. What's the internal diameter and width of the bearing, or just the number on the bearing?

5179

Did you add the springs to it as I suggested?

deannos
08-01-2012, 11:18 PM
The bearing nut thingy (picture below so everyone else knows what we're talking about!) should work better on a trapezoidal screw than the M16x2 threaded rod you're currently using. Just need to make sure it's the right size to engage properly. What's the internal diameter and width of the bearing, or just the number on the bearing? 5179 Did you add the springs to it as I suggested?[/QUOTE Thanks for the reply Jonathan, I've not used springs and it seems ok, i will check the bearing tomorrow for a number. The pc running everything gave up today so i went and had a few pints instead. Only just realised what you were saying about the price, i.e trap screw against a ball screw:redface: