Hi Guys

Having major dificulties tracking down any 10tpi Acme here in oz... I can however get hold of trapezoidal TR 20x4 which gives me roughly 6tpi.

Now for the question. Why is 10 tpi considered the standard in all of the reading I have done on these forums?

Why couldnt TR 20x4 be used ie 6tpi??? or at least why shouldnt it?

Look forward to advice.

Cheers Mark

You don't have to follow the crowd. Varying Tpi and transmission ratio lets you achieve the same goal in numerous ways.

Carel

So is there a reason that most go for 10 tpi???

Availability? Like you experienced in reverse? And if your metric down under, go metric to avoid exotic parts.

Carel

Same with the Acme - 6TPI is available in a few places in aus. After that it's the 20 tpi.

Logically, if your steppers can turn it you can run them slower to achieve the same movement.

Assuming my non-engineer and inexperienced CNC maths is correct this would yield a theoretical accuracy of 0.0008' (0.02mm), realistically a little less allowing for backlash etc. Compared this to 10tpi which would yield an accuracy of 0.0005' (0.01mm). The difference is to my mind negligable.

I imagine the steppers would be working a little harder to turn the rod, I haven't a clue what the formulae is to calculate the torque to force ratio's for comparison although I'm fairly sure some kindly soul will educate us on that shortly ;)

I'm guessing a slightly larger stepper may be required. We can pick up the 200oz/in steppers from a few places in aus for approx $80 per.

Cheers
Jason.

Assume 10 tpi = 2.54 mm/rev. Torque with 4mm and same configuration: = 2.54 / 4. With a gearing of 254/400, 127/200 = 0.635 the result is the same. This calculation is of course without the normally used moonshiftcompensation :).

Carel

I'm guessing a slightly larger stepper may be required. We can pick up the 200oz/in steppers from a few places in aus for approx $80 per.

Cheers
Jason.

WOW.... Where are you scoring these steppers from??? and on another note... if the rod was to be 18 or even 20mm dia, would the 200 oz/in be adequate to drive say a 1.5 meter lead??

Cheers Mark

Carel..Assume 10 tpi = 2.54 mm/rev. Torque with 4mm and same configuration: = 2.54 / 4. With a gearing of 254/400, 127/200 = 0.635 the result is the same. This calculation is of course without the normally used moonshiftcompensation .

HUH??? :) not sure what you are comparing here Carel........ Country boy here remember :)

Sorry, looking back it's a little obscure. I can always excuse for the language.;) Okay, assume you want to travel a distance of 4 mm. For the 4 mm you need 1 revolution, for the 10 tpi 1.57 revolution. For this travel you need an amount of energy. The energy of your motor stays the same. The time stays the same. So if you make a reduction from the motor so that the rod makes 1 revolution (for 4 mm) and the motor 1.57 revolution everything stays the same. Energy, time and distance.

If you are a country boy, ever thought of a GPS controlled router?

Carel

.....If you are a country boy, ever thought of a GPS controlled router?Carel

I think they have them in the Canadian Prairies; except the cutter runs horizontally and they call them ploughs.

If you're going to do Imperial machining, definitely use 10 TPI or 20 TPI. Why? Do the math.

For each turn of the screw, the nut moves 0.100" for a 10 TPI. For a 20TPI, the motion is 0.050" per rev.

It is a lot easier to do the math (in head or on paper) than with the 0.166666666"/rev of the 6 TPI or some other odd ball thread unless it is 8 TPI (0.125" per rev).

All the other explanations eventually pertain but this is why I'd pay to use 10 TPI or 20 TPI instead of a free anything else (unless it was 8 TPI, but only if I couldn't get 10 or 20).....

Is there somewhere that I can go to get the calculations to figure the mechanical advantage of a trapazoidal screw with a given motor. I have a 4 start, 8tpi coated screw and was wondering how much force that could be generated by using it.

[QUOTE=NC Cams]If you're going to do Imperial machining, definitely use 10 TPI or 20 TPI. Why? Do the math.
QUOTE]

So the bottom line is there is really no "One" reason to use or not to use any particular thread.

As I prefer to work in metric and as .02 of a mm is acurate enough for my purposes then there is no reason not to go with the TR18x4.

Thanks guys for the input... Will order it up this morning.

Cheers Mark

i use 6 tpi primarily to gain the extra speed any amount of torque loss is too small to say there is any , with 6 tpi your nearly doubling the speed as to running 10tpi , for a cnc router to cut wood what do you need for accuracy , i m going to be connecting geckos , the resolution is going to be .00008 , my last driver which was full step gave me a resolution .0008 which is plenty in my eyes ,and it ran very well , personally i see it as being a waiste of motor energy to run at a higher tpi

Just ordered 1.8 m of TR14x4 and 1.8m of TR18x4 from Motion Technologies. $138 AU for the lot, will be here by the end of the week.... :) This Should give me plenty to experiment with.

Let me know your findings, I may follow with the 6TPI.

Oh - and you can get the 200oz/in bipolar steppers for approx $80 new from advanced automation in Sydney and Ocean Controls in melbourne to name two. It seems most automation shops can get them in and the price is comparable to the US given currency exchange and freight.

Agro.

Hi Agro...

Thanks for that mate, mentioned cheap steppers to the guy from motion tech and he quoted me min $180... pretty much the story from all round the country..... Have the 4 190's comming with the board and other electronics so am not stuck yet.

Ordered pretty much everything now, cleaned and greased the lathe, swept the floor, must be BUILD TIME !!!.. :)

Cheers Mark

Trapazoidal just arrived at my work!!! WAHOO... only problem is I cant knock off and go home now !!!!

The Adventure begins. :cheers: