[MetalShavings]

I was wondering:

I've been working on the learning curve of using High Speed Machining with my Tormach 770 mill. Right now I can finish most parts projects only slightly faster using HSM as opposed to using the conventional machining method I was using before. This is mainly due to the power limitations of the 770 hobby mill.

So I was wondering if changing the drive belt to the larger-lower RPM pulley would offer any benefit in terms of speed when using High-Speed-Machining methods? If so, what would be the difference in torque value from one pulley to the other?

Using HSM with my drive belt being driven by the 10000 RPM pulley; while working with metals other than aluminum, I find I have to reduce my software calculated WOC's and myDOC's by at least a third in order to keep from straining my machine or bogging down to a stand still or a tool breakage. I've checked my users manual but can find no reference on wether there are any torque changes if one changes from one drive pulley to the other.

If the larger pulley gives more torque and the maximum RPM given by the larger pulley is close to the "Speeds" calculated by my HSMAdvisor software, might this be the way to go rather than having to reduce my WOC,s and DOC,s to keep from bogging down or slowing down the overall time savings that HSM was designed to overcome?

If higher torque values allows me to make deeper cuts, both axial and radial while maintaining the software's calculated spindle speeds, in my mind, this should speed my machining times up substantially. The problem is, I don't know if torque values change when going from one drive pulley to the other.

MetalShavings

[Al_The_Man]

RPM is reduced by the ratio of the reduction and torque increases by the same ratio.
Al.

[pickled]

Short answer to your question is YES. If you are in the low range RPM band for the material/tool then use the low pulley and you will be much happier with the performance. From my experience the 770 spindle will stall easily and/or lose RPM if you don't "downshift" to RPM match when working with pretty much anything besides aluminum alloys. I think that you will be pleasantly surprised with the results of the low range. I was always wondering why hardly any one that was YouTube splaining these machines were never changing out of Hi range? I do belt range changes often with both the 1100 and the 770 while I am machining. Just be sure to add belt change required to your G-code comments at tool changes so you don't forget to swap it back! I will sometimes forget to click the range change boxes on the control software, but the difference is usually pretty obvious before you get into the cut.

[MetalShavings]

Short answer to your question is YES. If you are in the low range RPM band for the material/tool then use the low pulley and you will be much happier with the performance. From my experience the 770 spindle will stall easily and/or lose RPM if you don't "downshift" to RPM match when working with pretty much anything besides aluminum alloys. I think that you will be pleasantly surprised with the results of the low range. I was always wondering why hardly any one that was YouTube splaining these machines were never changing out of Hi range? I do belt range changes often with both the 1100 and the 770 while I am machining. Just be sure to add belt change required to your G-code comments at tool changes so you don't forget to swap it back! I will sometimes forget to click the range change boxes on the control software, but the difference is usually pretty obvious before you get into the cut.

Thank you gentlemen: I suspected this might be the case but being that I've never seen it done when using HSM; heck I never even heard of this being suggested, I'll have to re-caculate my feeds and speeds using my lower RPM drive pulley.

I also figured that there might be a mathematical calculation that could shed some light on the change in torque values from one pulley to the other but, I absolutely SUCK at math so for me this avenue of figuring out torque ratios was to far out of the realm of possibility; and it's probably just a simple equation too. It sucks being mathematically challenged.

I don't suppose either of you guys have those differing torque values for the upper and lower pulleys on the 770 mill?

MetalShavings

[Zetopan]

I don't have a 770 (1100 owner here) but I did just examine the 770 owners manual for you and the high spindle speed range is 3X faster than the low speed range (actual ratio with both at minimum RPM is 3.0X and with both at maximum RPM is about 3.08X). Hence the low speed range will have 3X the torque available as the high speed range when the spindle motor is operating at the same RPM for both ranges.

Also be aware that above 60 Hz the spindle motor is essentially constant power (higher RPM = less torque) and below 60 Hz the spindle motor is constant torque (lower RPM = less power).

[MetalShavings]

I don't have a 770 (1100 owner here) but I did just examine the 770 owners manual for you and the high spindle speed range is 3X faster than the low speed range (actual ratio with both at minimum RPM is 3.0X and with both at maximum RPM is about 3.08X). Hence the low speed range will have 3X the torque available as the high speed range when the spindle motor is operating at the same RPM for both ranges.

Also be aware that above 60 Hz the spindle motor is essentially constant power (higher RPM = less torque) and below 60 Hz the spindle motor is constant torque (lower RPM = less power).

OK so, if my 770 is presently listed at 1.3 pounds of torque using the upper faster RPM drive pulley then by switching to the larger and lower RPM drive pulley I can generally assume that the math makes my torque go up to about 3.9 foot pounds correct?

When we throw in that 60 Hz snafu, would it be safe to compensate for that by just rounding the torque value down to an even three foot pounds when running on the lower RPM drive pulley?

MetalShavings

[SCzEngrgGroup]

Torque will scale by exactly the ratio of the pulley diameters. Double the driven pulley diameter, and you will double the spindle torque, while halving the RPM. Power is constant. Always. So, you might get more torque, but find you are now power-limited, rather than torque limited.

Regards,
Ray L.

[MetalShavings]

I've sent off an email to Tormach asking them if they can give me the torque specs when the larger of the drive pulleys is being used. Although insightful and most likely true, the answers I've gotten here are not registering with my mathematically challenged brain.

I tend to interpret them as saying that the answer to my original question is "Yes" but, It comes with a caveat. The HSM software I'm using calculates feeds and speeds by entering (among other things) the maximum spindle speed and the torque value as my machine is set up. That's easy enough to do when I've got my 770 mill set up to run with the smaller and faster drive pulley because Tormach includes that information in their users manual. All I'm looking for now is the torque values in foot pounds when using the larger of the two pulleys so that I can enter that information into the appropriate text field of the software in question.

From there this same HSM software can then calculate what I hope will be a set of more efficient feeds and speeds. By "Efficient" I mean, capable of decreasing the time it takes to machine the small parts I'm making without bogging down my mill while at the same time increasing the overall tool life I've been getting.

MetalShavings

[pickled]

It's a constant optimization game. FYI if you are using variable helix cutters you will want to give yourself the most torque advantage that you can at a given RPM. Anyway the math is basically derived from HP = (RPM* TRQ)/5252. Therefore
(HP*5252)/RPM=TORQUE FTLBS. So if you have a 1 HP motor and you are running at the rated 4000 RPM then it's (1*5252)/4000. So that would be 1.313 FTLBS of torque. Based on what I learned back in the day the pulley ratios are just like Ray L. stated. So hypothetically let's say that the 770 has a 3 inch driving pulley coupled to a 5 inch driven pulley this will change the RPM now via 4000RPM*(3/5)=2400RPM at the Spindle. Now go back and calculate (1*5252)/2400= 2.188 FTLBS of torque. Now I'm kind of fried tonight, but I'm pretty sure that my math is OK and I know someone smart will be reading this as well. FYI- according to what's in HSM advisor the HP Curve for a 770 in high range is based on these values....
RPM Power Torque
525 0.1 1
2000 0.5 1.31
4000 1 1.31
8000 1.01 0.66
10025 0.74 0.39

Once you know the diametric ratios of the pulley you can use this data to figure out when it's best to change the belt setting.

Please realize that every cutter and material have an SFM range that works best and provides for optimal feed rates. This is true whether you are using HSM or traditional tool paths...it's just physics and material science playing together to keep us honest. There may be no benefit to slowing the RPM down via belt reduction if it's going to drop you out of the ideal SFM for the tool/material combination you are working with. HSM Advisor and G-Wizard calculate the torque and HP required to make any given cut and typically have good starting SFM's to base your starting RPM on for any given material. I know that HSM advisor does a pretty good job of yelling at me when there is no way in hell I could ever make a given cut with my machines :-). When an HSM strategy doesn't work as the software says it should I typically have to go back and look at my toolpaths because they are usually the root cause. Sharp corners, poor tool engagement angles, aggressive ramping and/or little room for chip evacuation (re-cutting) are usually the culprits that end up blowing my HSM plans out of the water. Let the software packages handle the routine math while you just do your best to understand the concepts and you will get there soon.

[zero_divide]

I've sent off an email to Tormach asking them if they can give me the torque specs when the larger of the drive pulleys is being used. Although insightful and most likely true, the answers I've gotten here are not registering with my mathematically challenged brain.

I tend to interpret them as saying that the answer to my original question is "Yes" but, It comes with a caveat. The HSM software I'm using calculates feeds and speeds by entering (among other things) the maximum spindle speed and the torque value as my machine is set up. That's easy enough to do when I've got my 770 mill set up to run with the smaller and faster drive pulley because Tormach includes that information in their users manual. All I'm looking for now is the torque values in foot pounds when using the larger of the two pulleys so that I can enter that information into the appropriate text field of the software in question.

From there this same HSM software can then calculate what I hope will be a set of more efficient feeds and speeds. By "Efficient" I mean, capable of decreasing the time it takes to machine the small parts I'm making without bogging down my mill while at the same time increasing the overall tool life I've been getting.

MetalShavings

Tim,
If you get any good info from Tormach guys be user to share it with me. They did help me years ago build the power curve for their motors but perhaps they got better data since then.

Any way using the old data I made a new lower range machine profile for you. And it seems that at RPM 4500 and more you still better off with the high-speed pulley.

You have tiny mill and I suggest trying machinig with smaller cutters. You would be surprised how fast a 1/4" 4 flute carbide cutter can move material.

[MetalShavings]

Hi Elder:

According to my users manual the spindle speeds I can expect using the larger drive pulley are 175 minimum and 3250 RPM maximum. All I was after with my inquiries was a Torque number I could enter into the appropriate text field in the software's machine edit page. I figured it would just be a number like the torque value number "1.3" foot pounds supplied by the Tormach users manual when using the smaller drive pulley. From there I can trial-and-error my way to the outcome I'm looking for. I never really thought it would become as complicated as it's become for me. (perhaps not complicated for you but, for me)

I believe that those guys who were gracious enough to take the time to post replies containing mathematical equations know what they are talking about but, I don't have a clue. To me, looking at those mathematical equations is like trying to read Egyptian Hieroglyphs. I've mentioned this before but I must be sounding like I'm exaggerating or over dramatizing; I SUCK at math and I SUCK at reading Egyptian Hieroglyphs. I wish I could; this process would go a whole lot smoother for me.

At any rate, I thank you all for taking the time to post replies. I'll let you know what Tormach has to say about the torque values I've been searching for once they've replied to my inquiry. I'm hoping they don't go into a lecture-mode with their reply and further complicate things for my mathematically challenged mind. All I need is a number like the number they provided for the smaller drive pulley.

MetalShavings

[popspipes]

My rule of thumb is if you cut the rpm in half the torque doubles
The same applies in reverse, double the rpm and the torque gets cut in half
This is for gearing or belt driven situations

The inverter speeds will also affect this
In my case, I would try it and see if it works

There are other factors that have a bearing on this as well.

This works for me................

There is a place for engineering and math etc, but you still have to try it to see if it works in the real world, what works on paper doesnt always work in the actual application

[SCzEngrgGroup]

Hi Elder:

According to my users manual the spindle speeds I can expect using the larger drive pulley are 175 minimum and 3250 RPM maximum. All I was after with my inquiries was a Torque number I could enter into the appropriate text field in the software's machine edit page. I figured it would just be a number like the torque value number "1.3" foot pounds supplied by the Tormach users manual when using the smaller drive pulley. From there I can trial-and-error my way to the outcome I'm looking for. I never really thought it would become as complicated as it's become for me. (perhaps not complicated for you but, for me)

I believe that those guys who were gracious enough to take the time to post replies containing mathematical equations know what they are talking about but, I don't have a clue. To me, looking at those mathematical equations is like trying to read Egyptian Hieroglyphs. I've mentioned this before but I must be sounding like I'm exaggerating or over dramatizing; I SUCK at math and I SUCK at reading Egyptian Hieroglyphs. I wish I could; this process would go a whole lot smoother for me.

At any rate, I thank you all for taking the time to post replies. I'll let you know what Tormach has to say about the torque values I've been searching for once they've replied to my inquiry. I'm hoping they don't go into a lecture-mode with their reply and further complicate things for my mathematically challenged mind. All I need is a number like the number they provided for the smaller drive pulley.

MetalShavings

There is no single number you can use. Torque is a function of many things, not least of which is RPM. Your spindle is driven by a 3-phase AC motor, driven by a VFD. The fundamental (ideal) characteristic of such a system is constant torque below the motors "base speed", and constant power above base speed. I have no idea what the base speed of the motor used in the Tormach is, but it will be indicated on the motors nameplate. Let's assume the motor has a base speed of 3450 RPM, with a nominal rating of 1HP. With a 1:1 pulley ratio, that means your spindle torque, at base speed will be:

Torque = HP * 5252 / RPM = 1.0 * 5252 / 3450 = 1.5 ft lbs

In theory, this torque would be available all the way down to 0 RPM ,but in practice, below about 30% of base speed (~1100 RPM), torque will start to fall off rapidly. Power will fall off linearly as RPM is reduced, so at 1750 RPM, you'd still have ~1.5 ft-lbs of torque, but only ~0.5HP.

Above base speed, torque falls off linearly with increasing RPM. So, at 7000 RPM, you'd have only about 0.75 ft-lbs of torque, but still ~1.0 HP.

Here are the "idealized" torque and power curves for a theoretical motor+VFD. The actual curves for any real-world motor+VFD will be different, especially near both ends of the RPM range, but the only way to know what they actual curves are is to measure them on the target hardware.

Idealized 3-Phase Motor and VFD Torque vs RPM / Power vs RPM Curves

Changing pulley ratios will either increase torque, while decreasing RPM, or decrease torque, while increasing RPM. Torque, and power, will still change, at different RPMs, as outlined above.

Regards,
Ray L.

[Al_The_Man]

If the input RPM/Torque remains constant, implementing various reduction methods will increase the torque by the rate of reduction, the only basic time that torque will vary dependent on the particular motor rpm/torque curve.,.
Also one advantage as you go with higher reduction the motor to load inertia ratio improves at a rate of the square of the reduction, for e.g. with a servo this ratio is ideally no higher than 10:1.
Al. ,

[MetalShavings]

Following is a cut-and-paste of the reply I just got from the Tormach customer service guy:


"Good morning Tim,

We do not have a torque value for the different pulleys or the spindle itself because the torque varies throughout the range of the motor’s RPM in a parabolic manner that is somewhat dependent on your environment. The best way to find the value you seek is to perform cutting tests and calculate your torque from those variables once you stall out the motor and that will give you your max torque. Please let me know if you have any other questions. Thank you very much for your time and have a good day."

To which I have replied with one last email:

Hi Joe Gray:

And thanks for getting back to me. It's difficult to believe that you don't have or haven't calculated the torque when using the lower drive pulley on the 770 mill. How did Tormach arrive at the "1.3 ft. pound" value for the smaller 10000 RPM drive pulley? I figured you'd be able to at least estimate the torque of the Lower RPM drive pulley using the same formula.

I'd do it myself but I'm mathematically retarded. I'm good at alot of things but math isn't one of them.

Just for the sake of simplicity, lets say that the tormach 770 mill only had the one Lower RPM drive pulley. Can you tell me what kind of torque I could expect to get out of it if I ran it at the middle of the RPM range? My users manual says that with the lower pulley in use the spindle speed ranges are 175 to 3250 RPM. That would mean that around 1600 RPM or so, would be the midrange for that particular pulley.

Tim

[David C. Allen]

Thanks to Greg Jackson and Matt Doeppers from Tormach, and HSMAdvisor user (David C. Allen) who made a request, i was able to create Horse Power/RPM curves for Tormach PCNC770 and PCNC1100 models (if you install over previous version, you can use import function to add those machines to the list)
Currently there are curves for both machines, but only series 3.
Adding

This How import works

Also Threading page was added with ISO/UNC/UNF threading and tapping info


Here is the download page HSMAdvisor : Download

Huge thanks to everybody who helped with feture requests and bug reports :cheers:

So someone at Tormach has the information ! ! !

David
Tormach 1100 Series 3

[MetalShavings]

You guys are the best. I appreciate your input but, I have to tell you about the variables that I'm up against while trying to learn how to use HSM. I have very little free time in which to machine the small parts that I have to keep in stock for my inventory. I can either use up that free/spare time trying to figure out how to calculate torque values which will keep me from restocking my inventory or I can restock my inventory of small parts using a combination of conventional milling methods and the small amount of knowlege I've learned about HSM. I'll tackle the HSM learning curve as time permits.

I've chosen to run the parts with the means I have at my disposal before I no longer have that spare time with which to do it. The parts in question have now been machined and my inventory has been restocked for now. In a couple of weeks I'll have to do it all over again. I had hoped to have figured out this HSM thing so that I could make these parts runs in a minimal amount of time. This time around I used what could best be described as a hybrid version of HSM. That is; I used certain attributes of HSM but being that my Tormach 770 is limited in power, I still have to make shallow WOC's so in the long run my parts are being machined only slightly faster than if I were using balls-to-the-wall conventional machining methods.

I'm not complaining. I'm happy to have been able to reduce my machining time by even a small amount. With further trial-and-error testing, I hope to cut that time down even further. I was really hoping that by using the larger drive pulley on my 770 I could increase the torque enough to be able to make deeper cuts and thereby reduce the time it took to run my parts but, it seems that deeper cuts with slower spindle speeds is about the same as shallow cuts with higher spindle speeds. Time-wise, no matter which pulley I use the outcome is about the same.

Thanks guys. I'll keep plucking away at it.

MetalShavings

[SCzEngrgGroup]

Rather than trying to understand it, why not simply make test cuts, trying different RPMs, different pulleys, etc. It shuld not take more than a few hours to find the "sweet spot" for your specific parts. Even once you understand all the variables, and all the math, it's STILL necessary to spend time on test cuts to validate the calculations. I ALWAYS do that whenever I start using a new tool, or new material, or new methods.

Regards,
Ray L.

[MetalShavings]

Rather than trying to understand it, why not simply make test cuts, trying different RPMs, different pulleys, etc. It shuld not take more than a few hours to find the "sweet spot" for your specific parts. Even once you understand all the variables, and all the math, it's STILL necessary to spend time on test cuts to validate the calculations. I ALWAYS do that whenever I start using a new tool, or new material, or new methods.

Regards,
Ray L.

The "Few Hours" that you're alluding to is the very same time reference I allude to when I mention "Free-Time" or "Spare-Time." This "Time" is at a minimum with me so it was my hope that by getting a handle on this HSM method I could more efficiently utilize what little Free-Time I have to work with.

My method of learning is known as the "Trial And Error" method. For the most part, it too is basically the same thing you're are talking about when you suggest "Test-Cuts." And in fact, I do that very thing as time permits. By asking for Torque values I was hoping that if someone actually had those values in number form, I could simply use them as a short cut to having to figure it out myself by means of Trial And Error or multiple Tests-Cuts. I see now that there really are no such numbers; at least not in the form that I had hoped. There are to many variables that play into it so, I'm relegated to doing what I can in the time I have to do it.

Thanks Ray L.

MetalShavings

[pickled]

The "Few Hours" that you're alluding to is the very same time reference I allude to when I mention "Free-Time" or "Spare-Time." This time is at a minimum with me so it was my hope that by getting a handle on this HSM method I could more efficiently utilize what little Free-Time I have to work with.

My method of learning is known as "Trial And Error" method. For the most part, it too is basically the same thing you're are talking about when you suggest "Test-Cuts." And in fact, I do that very thing as time permits. By asking for Torque values I was hoping that if someone actually had those values in number form, I could simply use them as a short cut to having to figure it out myself by means of Trial And Error or multiple Tests-Cuts. I see now that there really are no such numbers; at least not in the form that I had hoped. There are to many variables that play into it so, I'm relegated to doing what I can in the time I have to do it.

Thanks Ray L.

MetalShavings

Hey man there is nothing wrong with doing it the way that you are doing it now. If anything pushing towards a little more HSM approach will at least let you use more of that nice cutting edge and get your money's worth out of the tooling you have bought right :-)? In situations like yours there is a cool concept called evolutionary operations (EVOP) that a smart guy named George Box came up with. I've used it (and many other tools) a lot over the last few decades to stay sane under pressure LOL. Basically EVOP s a highly systematic way to conduct multi-variate experimentation while you are running the production instead of dedicating your machine to R&D.

Unfortunately there is a lot of mathematics involved in doing it the "official correct way", but the concept of performing small experiments on each production batch to, hopefully, optimize over time is quite valid. It may be a good strategy for you. At any rate, I sincerely hope that you knock out that next batch with less time taken off the clock! I feel you on the time constraints. I had a horrible day here and ended up reworking a finished part that developed a case of excessive run-out after welding the final assembly. I saved it, but lost 5 hours...do you happen to know where a guy could buy some midnight oil? Take it easy.