[CROSSHATCH]

I wasn't planning on using Ballscrews. Yes I know you reduce the torque by 50 percent.

I never planned on cutting at 20+ IPM unless I took down the DOC. Oh and I planned on upgrading the motor too a 3/4 horsepower, maybe even 1 Hp motor anyway this summer.


You also have too know that Taig cut back on many things too keep the machine in the price range. They could have designed other components but that would make the machine twice as expensive. It's not really about the engineering obstacles, but rather the reason they did it, was for the cost factor.


It's an idea i'm toying with anyway, maybe I won't do it. Just something I was thinking about.


-Jason

[jalessi]

Jason,

The reason why Taig is using 20 TPI screws verses 10 TPI screws has nothing to do with cost.

You must be joking.

Its a matter of enhanced resolution, accuracy and increased torque IE overcoming the resistance of the ways.

Jeff...

[jalessi]

Jason,

By the way, Taig has not cut back on anything.

For its size it is over engineered.

Jeff...

[CROSSHATCH]

No, i'm not saying as far as there TPI goes. I know it's there for accuracy. I'm saying that overall, i'm sure things were done in certain ways while still being very effective too cut some cost down.


The machine is beautifully engineered, minus the way the spindle motor is mounted, other then that. It's a great machine. Thats why I bought it.


-Jason

[Fixittt]

I believe that what jeff is trying to explain to you is that there is a trade off. speed vs resolution. Cant really have both. by increasing the resolution you reduce speed. Simple math. Also the design of the Taig, maxnc sherline alike, the machines will wear terribly if you increase the speeds. Trust me I know. Your wanting faster rapids I understand that. But why sacrifice the machine to achieve this? I know you want the machine to zip around because its cool. Its only going to cut down on machine time a fraction. I have been where your at and I soon realized that getting a good part the first time at a slower speed was worth more to me then trying to force the issue and having to run the part 3 or 4 times before it came out right.

[CROSSHATCH]

I understand where Jeff is coming from. I understand his points. I really only want too increase my speeds barely. I'm only running 6 IPM rapids MAX. Thats a little too slow. I know what I want too rapid at and don't believe it will do that much damage. Heck, you say you cut in wax at 20 IPM? I'm cutting 3 IPM in aluminum.

I only wanna rapid slightly more. But hey, the Gecko drivers will take care of that.


-Jason

[Hirudin]

Hmmm... at the risk of jalessi ripping me a new one: I don't think adding ball screws is that preposterous of an idea. It's one thing if they wont fit, that's a hurdle that is much more difficult to overcome, but wanting the machine to move faster sounds like a goal we can all get behind (even if it only means the rapids will be faster).

Sure, going from 20 to 10 TPI is going to halve your resolution, but will that make any real world difference? If you're using 10x micro stepping that's 2000 steps per revolution, if it takes 20 revolutions to move an inch that's 40,000 steps per inch (or 0.000025" per step), talk about overkill. Having 25 millionths of an inch accuracy on a machine using collets that may have a TIR of 200 millionths seems a bit silly, no?

[jalessi]

If you're using 10x micro stepping that's 2000 steps per revolution, if it takes 20 revolutions to move an inch that's 40,000 steps per inch (or 0.000025" per step), talk about overkill. Having 25 millionths of an inch accuracy on a machine using collets that may have a TIR of 200 millionths seems a bit silly, no?

Hirudin,

I don't mind being corrected, however there is a very big difference between two hundred-thousandth's and twenty five millionth's.

If all you are after is a speed or feed increase a simple pulley and bracket arrangement would double the speed-feed for less than $20.00.

It would be a lot easier than retrofitting the screw also.

Thanks for the lesson,

Jeff...

[Stepper Monkey]

I have very seriously looked into doing a ballscrew conversion, and yes, it is possible and has even been done. It is not at all practical however. Looking over what needed to be done (quite a bit actually), I rapidly decided it was just not worth it. Add in the cost, and it starts to look like it is easier and cheaper to either a) build a new mill from scratch using the stock Taig to make the parts, or b) get a different machine that has them already.

Adding A/B nuts however, either homemade or from someplace like Kerk, is very easily done actually. Turning two different diameters to one end of each screw, and threading the ends of them, is all that needs to be done. Adding the mounting adapter for the nut is trivial.
Pitch change can happen then if you like just as easily.

As for pitch change, the resolution lost is actually pretty irrelevant considering the machines repeatability and tolerances.
The loss of half the torque to gain speed is not necessarily true here, as you also have to realize the motor is spinning half as fast. Depending on where the torque/speed curve and inductance of the motors is, you can optimize for anything. Given the same drivers you could take two machines, one at 10 tpi and one at 20 tpi, and get exactly the same performance by simply getting two sets of motors with different inductance and oz/inch ratings. There would be no gain to that other than you could then use a lot more of the commonly available motor winding configurations (which tend toward almost stupidly high inductance) if you had 10 tpi!

[Fixittt]

another way of getting the same performance out of the two exampled machines (one with 10 tpi screws and one with 20 tpi screws) is to set the one with 10 tpi to 1/8 microstepping and the one with 20 tpi screws to 1/4 microstepping. if your drives allow that adjustment. everything else being identical

Food for thought.

[jalessi]

Stepper Monkey,

If the stepper motor remained the same and you changed the drive screw from 20 tpi to 10 tpi it is changing the gear ratio by fifty percent.

No matter how you look at it the torque would decrease by the same amount.

What you are promoting is a total fairy tale and just not true.

Jeff...

[Hirudin]

I'm not masquerading as an expert, and I'm not trying to give a "lesson".

Did I get the terminology wrong? Isn't "0.000025" also called "twenty-five millionths"?

All I wanted to say is that the "loss" of resolution doesn't seem relevant when you're only moving from 1/8 of the runout of the collet to 1/4 of the runout.

Stepper Monkey, are you referring to my attached image (the torque curve of the exact motors SpeedsCustom is using)?
So, with a stepper motor, reducing the pps (Pulses Per Second, right?) by half will also roughly double your torque. So, at half the RPM you have somewhere around twice the torque.

So, if you BOTH double your torque by spinning your motors at half the RPM AND halve your torque by doubling the screw pitch, aren't you left with roughly the same speed and roughly the same torque?
1 * 2 / 2 = 1

Why would anyone want to do that? Well, because the motors will STILL be able to turn at higher RPM, so when you have a low torque requirement (like during rapids) you could get much higher IPM. The only problem is, you loose resolution, but going from 0.000025 to 0.000050 doesn't seem like that big of a deal to me.

Now, if ball screws wont fit, they wont fit... If you think they're a stupid idea for that reason, fine. Why bring up all the other stuff?

[Stepper Monkey]

If the stepper motor remained the same and you changed the drive screw from 20 tpi to 10 tpi it is changing the gear ratio by fifty percent.

You are correctJalessi. That wasn't what I was trying to get at getting at though - hence the "get exactly the same performance by simply getting two sets of motors with different inductance and oz/inch ratings" part of the post. If the motor remained the same you would indeed be changing the gear ratio.
The two machines would of course have to have two radically different sets of motors at that point to behave the same way. But they could at that point behave the same way

My point was simply that you could build/optimize for about anything. The TPI doesn't mean a whole lot all by itself, it is not an absolute fixed determination of the overall machines speed/torque envelope, but just one of them. Depending on inductance, and as Fixitt pointed out, microstepping, you can offset or add to the changes or effects of any of these other variables. They are all interrelated.

[hydropro]

I'm using Intelligent Motion IM483 Micro stepping drivers with 200oz Pacific Scientific Powermax II motors and a 40v 10a unregulated power supply on my Taig Mill and my rapid speed are a consistant 60ipm with no lost steps.