Belt Drive Conversion

**RustedOut** · 10-12-2011, 09:58 PM

Not really Mike, just finished the fab work on 3 motorcycle lifts and delivered them to the blasters today. That was about two solid weeks of work. I'll get them painted in the next week and finish my wife's fab project, then may find the time to get back to the back gear design. Had a bunch of other work needing done as well. Work load is starting to lighten up though I got some unfinished stuff out there, but now I got a lot of firewood to split. I'm busier now than when I had a job.

I did order and receive the new higher rpm spindle bearings this week. Did some research this morning on the seals I'll need to keep the oil in the gear box. I've decided that I will finish the back gear design, then choose between the two designs. The back gear is a lot of work, but offers so much more than the standard belt drive.

I have had lots of good conversations in the past few months about the concept of over speeding the inverter duty motor. Some are doing it with standard 3 phase motors. Those conversations are what lead me to pursue the use of a back gear. I'm sticking with the max 6000 rpm on the motor for now.

One thing that has to come into play with the belt drive conversion is an pneumatic auto draw bar. Had a long conversation with a friend the other night about it and came to the conclusion I'm going to use a hybrid Tormach style tool holders. I intend to add a piece to the end of the spindle to give me 2 lugs to help drive the tool holder. I'll add the slots for the lugs to my 3D models of my tool holders before I build them. This is a detail taken from Mr deCaussin. Not going the CatR8 route though. Intend to use his 900 lb pull Belleville washer stack and will design a 1200 lb cylinder to operate them.

On the splined bushing, I know a couple guys in the UK that I'm thinking of asking a favor of and ask if they will purchase and ship me a few of those $20.00 bushings. Can't believe it's that tough to get them in my hand, but every option so far has been expensive. I do want the splines in the new hub as they make it real easy to drop out the spindle for maintenance.

Bob

**SCzEngrgGroup** · 10-14-2011, 08:55 PM

Originally Posted by RustedOut

I'm going to use a hybrid Tormach style tool holders. I intend to add a piece to the end of the spindle to give me 2 lugs to help drive the tool holder. I'll add the slots for the lugs to my 3D models of my tool holders before I build them. This is a detail taken from Mr deCaussin. Not going the CatR8 route though. Intend to use his 900 lb pull Belleville washer stack and will design a 1200 lb cylinder to operate them.
Bob

Not sure what problem you think you're solving by keying the spindle and tool-holders, but you better get more familiar with the strengths, and weaknesses, of TTS-style holders. 900-1200# is less than half the drawbar tension required to use TTS-style holders to their limits - pull-out on aggressive cuts will be a significant problem with such low tension. That will work fine on a fractional HP machine, like a small benchtop mill, but not on anything even in the 1HP range. And once you DO have appropriate drawbar tension, the keys are completely unnecessary - if the holder can turn, it can also pull-out. Retain it properly, and neither is a significant issue, until you get up into the 2-3 HP range.

Regards,
Ray L.

**RustedOut** · 10-14-2011, 11:01 PM

Thanks for the advise Ray. Not sure how to get familiar without having hands on experience and can't get that until I jump in. My thinking is if I can keep them from turning, maybe I avoid pullout. But that's just a hunch from thinking about the lack of torsional control of the QCTH by the 3/4" collet. I reasoned that was the source of the problem overcome by Tormach with additional tension on the collet. All I have to study first hand is my current mill and there's a lot of torque at the cutter. I ran tool holders and R8 collets without the set screw key in the spindle for a few years without any hardships and I know I didn't put that much torque on the draw bar.

It's been quite a while since I read any technical info on the Tormach style tool holders, and it'd be good to go back and visit that before I get into that portion of my project. Maybe the additional tension is the way to go, and if so, I can surely add it in the original conversion. I've honestly been pondering the pneumatic cylinder more than the tool holders to this point, along with the back gear addition. It's had me stumped a time or two but I've just about worked through all the issues I think. Needs a bunch of refinement now. Still stumped by the cylinder design though as there isn't much room up there. Ever see Fadal's rectangular cylinder? I've been wondering if the shaft could be off center and still work correctly, doubt it. But lately been looking at some sort of bellcrank to make it work.

I have been messing around with some precision acme screws for a jack and know that the screw I chose for that generates about 1800 lbs force as I recall and I can drive it with a 12v cordless drill. Wondering if that could take the place of a pneumatic cylinder for the auto drawbar.

Bob

**SCzEngrgGroup** · 10-15-2011, 12:03 AM

Bob,

You can't compare drawbar requirements for TTS with R8, or ANY taper. An ISO30 spindle has a MAX drawbar tension spec of only about 1100#, and it's capable of supporting much higher machining loads than TTS. The taper GREATLY increases holding power, and you lose that with TTS, due to the straight shank. If it moves AT ALL, axially or rotationally, you're going to have problems. Constraining one, and ignoring the other will not do you much good. The TTS power drawbar puts upwards of 2500# of tension on the drawbar through a stack of Belleville springs. My attempt to build a suitable PDB about 3 years ago validated that number. There's also a white paper on the Tormach website documenting the testing they did to determine how to best retain TTS holders in the spindle.

Getting the needed force with a pneumatic drawbar requires a big air cylinder and/or some significant mechanical advantage. The simplest solution is an air-over-hydraulic system, which is what is commonly used on VMCs. For TTS, I'm building a PDB using a stepper motor and high ratio NEMA planetary gearbox. This will give me (through current limiting) 25 ft-lbs tightening torque (to get 2500# drawbar tension), and up to 75 ft-lbs loosening torque, from a 495 oz-in stepper motor. I'll be able to loosen the drawbar one turn for TTS tools, or unscrew it completely for R8 tools, so I can use both interchangeably.

BTW - The locating key in R8 has NOTHING to do with keeping the tool from spinning under load. That is a myth. It is purely a convenience for installing the tool. You can remove it, and it will make absolutely no difference whatsoever in operation. If the taper doesn't keep the tool from spinning, that tiny little pin sure as hell isn't going to help one bit - it'll just shear right off instantly!

Regards,
Ray L.

**Mark Housel** · 10-15-2011, 07:46 PM

It is purely a convenience for installing the tool. You can remove it, and it will make absolutely no difference whatsoever in operation.

I guess that's why all of the mills at school that folks had trashed the key on, were left without it.

I never noticed any difference and at least that way we didn't have trouble getting the collets in and out.

**RustedOut** · 10-16-2011, 12:18 PM

Originally Posted by HimyKabibble

Bob,

You can't compare drawbar requirements for TTS with R8, or ANY taper. An ISO30 spindle has a MAX drawbar tension spec of only about 1100#, and it's capable of supporting much higher machining loads than TTS.

Personally, I'd rather have a taper style tool holder system than the TTS version. I've intended to make all my tool holders anyway if need be. I have Mr deCaussin's 3D models for his CatR8 tool holders as well as the drawbar model to work from. My stumbling point with it is with the release of the tool holders and wondering if my current machining ability is good enough to produce them accurately. My R8's always need tapped out, some holders more so than others. Guess I'm kind of leery about going that route knowing there may be a problem getting the tool holder out of the spindle. Again, it comes down to having no experience with the things I don't already have. I have to bump out my MT centers on my lathe as well, but my Cushman 115 5C style collets get pushed right out with the screw action. I'd like to believe the CatR8 would work like them, just not sure.

Originally Posted by HimyKabibble

The taper GREATLY increases holding power, and you lose that with TTS, due to the straight shank. If it moves AT ALL, axially or rotationally, you're going to have problems. Constraining one, and ignoring the other will not do you much good.

Exactly what I've thought all along on the TTS style. That's why I figured it needs some help. My ER32 collets need to be torqued to 100 ft lb in order to hold the cutters adequately, larger cutters being more prone to slippage of course. But it seems Tormach chose to constrain only one, ignoring the rotational constraint except by squeezing it tighter in the collet. I understand why they did it that way, just wondering if additional rotational constraint wouldn't diminish the force needed on the draw bar. One Bridgeport QCTH system (Mach 1) I've looked at used additional clamping to the outside of the spindle for use with larger cutters. Their drawbar uses only a 600 lb die spring.

Originally Posted by HimyKabibble

The TTS power drawbar puts upwards of 2500# of tension on the drawbar through a stack of Belleville springs. My attempt to build a suitable PDB about 3 years ago validated that number. There's also a white paper on the Tormach website documenting the testing they did to determine how to best retain TTS holders in the spindle.

I intend to use the Belleville washer stack or similar as well, releasing them, for now, with a pneumatic cylinder. Problem is, once the belt drive components are added, there is little room for the cylinder. At least thats the state of my 3D models right now. How did you release the washers in yours?

Originally Posted by HimyKabibble

Getting the needed force with a pneumatic drawbar requires a big air cylinder and/or some significant mechanical advantage. The simplest solution is an air-over-hydraulic system, which is what is commonly used on VMCs. For TTS, I'm building a PDB using a stepper motor and high ratio NEMA planetary gearbox. This will give me (through current limiting) 25 ft-lbs tightening torque (to get 2500# drawbar tension), and up to 75 ft-lbs loosening torque, from a 495 oz-in stepper motor. I'll be able to loosen the drawbar one turn for TTS tools, or unscrew it completely for R8 tools, so I can use both interchangeably.

Using a pneumatic cylinder to provide the clamping force was never in my plans. Using it to release the clamping was. I've given a little bit of thought to a motor driving a screw, but only to unclamp the spring stack. That's why I mentioned the acme screw I've just used in my lifts. I like your thinking on the interchange of tooling and have wondered if I would ever need the old R8 stuff once I changed. My design doesn't lend itself well, if at all, to that interchange. But if done right, it shouldn't be an issue. See my last paragraph below.

Originally Posted by HimyKabibble

BTW - The locating key in R8 has NOTHING to do with keeping the tool from spinning under load. That is a myth. It is purely a convenience for installing the tool. You can remove it, and it will make absolutely no difference whatsoever in operation. If the taper doesn't keep the tool from spinning, that tiny little pin sure as hell isn't going to help one bit - it'll just shear right off instantly!

Regards,
Ray L.

I concur mostly with that statement, but do know that the MT shanks on my lathe drill chucks do benefit greatly from a set screw engaging a flat on the end of the shank. The bigger the drill bit, the more it is needed. My Cushman 115's use a key as well, but I've no clue as to the need for it. The MT's issues could be due to their slight taper vs the greater taper of the R8 tool holders.

One final thought, going back to the Mach 1 style QCTH's, maybe it's worth going just to pull studs on my existing R8 holders and custom making a releasing draw bar using Mr deCaussin's models as reference. Then I don't need to make a host of tool holders, only draw studs or buy them from Mach-1. Not intending to make a tool changer, so don't need the shorter tool holders. Modifications to my current lineup of R8 holders would be needed to keep the top end and pull stud where it needs to be, or purchase them from Mach 1. Sadly, they don't offer ER type collet holders but their modification service is affordable. But watching their video's, those tool holders pop right out of the spindle so maybe my fears are un-warranted.

Thanks again for the wisdom and advise. Lots more here to ponder.
Bob

**SCzEngrgGroup** · 10-16-2011, 01:07 PM

Bob,

Beware of optimizing things that don't need optimization. If your machine is in the under 2HP range (aren't all IH machines 1.5HP?), TTS is MORE than capable of supporting any operation you can reasonably perform, IF enough drawbar tension is provided. Tapered holders are great, but why go that route if you'll never be able to use the added capability because of other limitations in the machine? To release any tapered holder, you'll HAVE to provide some downforce, on the order of a few hundred pounds. If using a belleville mechanism, this downforce can be easily accomodated into the design of the release mechanism so that the first increment of drawbar movement compresses the bellevilles enough to release the tool (and the drawbar "floats" so no force is applied to the spindle, and beyond that limit the entire drawbar mechanism moves downward to create the force needed to pop the taper.

I would discourage you from thinking a machined taper would be an improvement over TTS in terms of holding ability. For a taper to work well, both surfaces must be VERY precise, and VERY smooth, creating essentially an air-tight fit. You'll never get that by any process short of precision grinding. Once you're forced to go that route, you'll find real tapered toolholders, like ISO30s, are a bargain. 30-taper holders have become MUCH more common, and MUCH cheaper, over the last two years or so, and are now available at prices not very much over R8.

Again, TTS can handle pretty much anything an IH can throw at it, so why try to improve what doesn't need improvement. I'm using TTS on a 3HP knee mill, doing some very aggressive cutting, and I've never had a tool come loose on me. The whole key is having ENOUGH drawbar tension.

Yes, the bellevilles are always used to CREATE the drawbar tension, but keep in mind the release mechanism MUST be capable of significantly GREATER force to release the tool, due to the non-linease belleville response, friction and other losses. My testing determined that this requires holding 2500# tension (from the belleville stack), and as much as 4000# to release it (particularly since the belleville force increases significantly as you further compress the springs to release the tool). For a pure pneumatic solution, you're talking a VERY large diameter cylinder (7-8"), or a multi-stage cylinder (like a 4" triple). I tried using a smaller cylinder, and mechanical force multiplier linkage, and the frictional losses are a killer. The release MUST be done by some mechanism that squeezes the belleville stack WITHOUT putting that force on the spindle bearings, as a 3-4000# static load is more than enough to damage the bearings.

There are some tools I already have, like my Glacern 4" R8 shank face mill, that I would not trust to TTS, so they will stay R8 (unless I switch to ISO30).

The key is useful in a lathe tailstock precisely because it DOESN'T have a drawbar. Even so, a whack with a deadblow hammer should lock the taper in place, making the key extraneous. With a drawbar, the key is completely useless, as the drawbar tension is there solely to ensure the taper is securely locked.

The Mach1 holders pop out automatically because ALL of the release force is transmitted through the spindle bearings, so the bellevilles will compress until the taper pops, then the whole drawbar and tool will move down, taking the load off the spindle bearings. The 600# of force required to release the belleville tension is more than enough to pop all but the most stubborn taper (like one that's been left in place for years), but not enough to harm the bearings. Again, it's the taper that ALLOWs the reduced drawbar tension to work.

Regards,
Ray L.

**SCzEngrgGroup** · 10-17-2011, 02:12 AM

Bob,

"I have Mr deCaussin's 3D models for his CatR8 tool holders as well as the drawbar model to work from." - I'd be interested in getting a copy of those, if you can. I'd like to see how to did the pull-stud "gripper".

Regards,
Ray L.

**RustedOut** · 10-17-2011, 01:22 PM

I picked up the 3D models from this site a year or more ago. I recall them being STL's, but could be wrong. Don't think I'd use leaded steel for the tool holders though, probably 4140 pre hard instead.

Actually the IH comes with a 2 hp, 9 amp, D80 metric motor. Mine will have either one of the two Baldor inverter motors I now have, a 3 hp or a 2 hp. My 68 year old lathe may need a motor swap down the road a bit, so thinking today the 3 hp gets saved for that use.

I realize if I build tapered tool holders, they should be ground. I have a taper attachment on my old lathe and could build a grinder attachment if needed. I really do like the CatR8 Mr deCaussin has come up with, just not sure I can repeatably pull that off with my current machining ability or if I even want to. I am getting better at splitting thousands on my lathe though. Taper style tool holders seem to be working with 1/3 to 1/4 the clamping pressure of the TTS system. That's a big plus in my thinking. That's where I was coming from when I said I was considering drive tangs with the TTS style system. Keep the clamping pressure as low as possible using something else to offset it. Has the TTS system ever been tested with positive drive tangs and lower clamping pressure? Thinking about it a bit more since our discussion started, I guess I'm not too thrilled about the lack of a direct connection to a draw bar as well with the TTS system. But again, no experience there so I'm speaking from a point of zero knowledge. Just wondering out loud.

I'd rather not go to that much drawbar clamping force if I don't need to. I just plain don't have room for a large pneumatic cylinder to un-clamp the drawbar when I convert the mill to a belt drive. Now a small air cylinder off to one side pulling a lever to turn a short acme screw for that pressure, yes probably doable. A linear actuator or solenoid in place of the pneumatic cylinder could work too. A 12v solenoid would be pretty fast and not need a steady air supply. Beyond the pneumatic cylinder space issue, I'd like to be able to un-clamp the drawbar by pushing it down without the need for a supplemental spindle or drawbar support, in other words, pressure right on the spindle bearings. If that's at all possible. A roller bearing can take quite a high axial load. So, again, low clamping pressure a plus there as well. The Mach 1 system allows that. Maybe I'm nuts on that subject though and have been playing with a model of a drawbar support. Looks like I can make that fit with the belt drive and possibly integrate the acme screw release into that.

This discussion has given me pause to take a longer look at the Mach 1 system. Thank you Ray for that. The long R8 tool holders don't cause me any grief as I have no intention to run an ATC. Mach 1's drawbar won't fit or function in my mill so I'd have to build it. Studying the needed mods to the tool holders shows me they just need to be a standard length as measured from the taper, but their $30.00 fee for modifying existing tool holders is pretty cheap too. I don't like running R8 collets, so I'd only be modifying a number of set screw holders, multiple ER collet holders, multiple Jacobs chuck arbors, face mill, boring head and saw arbors. Don't own a tapping head right now, but maybe that in the future as well. But basically keeping all my current tool holders in use. That's another big plus and new R8 stuff is dirt cheap for the most part.

This has been a very good conversation and I do appreciate your input and knowledge. I don't know today what direction I'll end up going, but you can probably tell what way I'm leaning right now. I'm not much into lists, but I can see where a list of demands and requirements would have been good at the start of my tool holder considerations.

All good points Ray, thanks for sharing.

Bob

**LUCKY13** · 10-17-2011, 04:27 PM

Rustedout,

if you did not grind the holders this allong would cause problems. Then you would need to blue the parts to check the contact between them.

Just looking at your design ( I know its Daves design to begin with) its possible the tapper might not be reaching full contact because of the end piece you put on the spindle. Its hard to really see in the pics, but if the end piece keep the holder from gonig all the way into the tapper it would cause problems.

It would surprize me if hardening made any differance. It would help them last longer, but if they where deforming from pressure I would be surprized.

The draw bar may have something to do with it also. You said yuo would add a extra bearing and this got me thinking with only the very short tapper the drawbar probably does help support it. This could mean the face of the drawbar & the top of the holder might need to be ground finish, plus be able to pull into each other with a good fit.

Seems to me you had it there, it just needed some bugs worked out. And I also like its design better than the Tormach. The Tormach system may work good but I believe a tapper would work better. I would give it a nother try and see if you could get it worked out. That would be a nice system. You can buy a system like this through Enco but its very expiencive. I believe it is Royal that has it and it looks just like Daves setup expect it has a collect you use much like the Tormach except its the R8 tapper with a stud. Thats the problem with trying to get a system working is the cost. If we could get one of the companies that get parts made over sea's to pick the design up and make them then it would be affordable.

IDK if this will take you right to it or not but here is a link.

Enco - Guaranteed Lowest Prices on Machinery, Measuring Tools, Cutting Tools and Shop Supplies

Like I said they do cost. But its different than any other system we have seen. It might even give a idea of how to make one. This system looks like it would hold a lot of power . It even claims it would hold %100 of the power. But I cant see it being worth the cost, although it could be used with any R8 spindle so it would not be restricted to one machine.

Jess

**SCzEngrgGroup** · 10-17-2011, 06:38 PM

Bob,

Ah! What you have is not Dave's drawings.... Those were done by one of the guys here on CNCZone, about a year ago, based on conversations with Dave. He abandoned the design, because he couldn't get it to work reliably, and the "grabber", in particular, seemed to wear very quickly.

Drive tangs still will not prevent pull-out, which is the major limitation with TTS. I've never heard ANYONE complain about the holders spinning, just pulling out under very heavy machining. Reduced drawbar tension WILL reduce the maximum cut you can take with TTS. There's simply no way around that - it's the price of not having a taper.

The way to avoid putting load on the spindle bearings is to apply the compressive force directly on the belleville stack - top AND bottom. Put a flange below the bellevilles, and another above. The PDB then engages BOTH. As the PDB compresses, the top flange will make contact, then the whole PDB rises up until the bottom flange makes contact. This puts ZERO load on the spindle bearings. Putting a limit on upward travel allows the last little but of PDB travel to be used to push down on the spindle to pop the taper, after the bellevilles have been compressed. It's mechanically trivial, and works perfectly. That's how I did mine, and I'm quite certain that's how the Tormach one works as well.

The $30 tool modification fee for the Mach1 system will almost get you an ISO30 holder. They're not that expensive anymore - only a bit more than R8.

**SCzEngrgGroup** · 10-17-2011, 06:42 PM

Originally Posted by LUCKY13

IDK if this will take you right to it or not but here is a link.

Enco - Guaranteed Lowest Prices on Machinery, Measuring Tools, Cutting Tools and Shop Supplies

Like I said they do cost. But its different than any other system we have seen. It might even give a idea of how to make one. This system looks like it would hold a lot of power . It even claims it would hold %100 of the power. But I cant see it being worth the cost, although it could be used with any R8 spindle so it would not be restricted to one machine.

Jess

At those prices, it would be cheaper to just got ISO30. The spindle is only a few hundred $, and the holders are a small fraction of the cost of those things, plus there's a much wider selection.

Note also from the Royal website:

"Please note that the Royal Easychange R8 Quick-Change Tool System is designed for light/medium-duty applications where the ability to change tools quickly outweighs the need for extreme rigidity. We do not recommend using this system for heavy milling or high-production applications."

So, it's no better than TTS, and very likely worse.

Regards,
Ray L.

**RustedOut** · 10-17-2011, 08:11 PM

[quote=LUCKY13;1008570]Hi Jess,

Not my web site. I just stumbled upon it some time back.

Them Royal QCTH's are real pricey. Royal makes some nice products though. They also extend the spindle which may not be a good thing.

Originally Posted by HimyKabibble

Bob,

Ah! What you have is not Dave's drawings.... Those were done by one of the guys here on CNCZone, about a year ago, based on conversations with Dave. He abandoned the design, because he couldn't get it to work reliably, and the "grabber", in particular, seemed to wear very quickly.

Drive tangs still will not prevent pull-out, which is the major limitation with TTS. I've never heard ANYONE complain about the holders spinning, just pulling out under very heavy machining. Reduced drawbar tension WILL reduce the maximum cut you can take with TTS. There's simply no way around that - it's the price of not having a taper.

The way to avoid putting load on the spindle bearings is to apply the compressive force directly on the belleville stack - top AND bottom. Put a flange below the bellevilles, and another above. The PDB then engages BOTH. As the PDB compresses, the top flange will make contact, then the whole PDB rises up until the bottom flange makes contact. This puts ZERO load on the spindle bearings. Putting a limit on upward travel allows the last little but of PDB travel to be used to push down on the spindle to pop the taper, after the bellevilles have been compressed. It's mechanically trivial, and works perfectly. That's how I did mine, and I'm quite certain that's how the Tormach one works as well.

The $30 tool modification fee for the Mach1 system will almost get you an ISO30 holder. They're not that expensive anymore - only a bit more than R8.

I believed 3D models were made from dxf files from Mr deCaussin, but I may be incorrect. Sorry, don't know the fellows name, but the link provided may provide that info. I'd nearly forgot where I got them, but found the bookmark I had made back then. I haven't spent the time making them fit exactly into my models as I have never finished the IH spindle model. That's on my to do list with a few other unfinished items involved in this conversion.

Now that I've mostly given up on a pneumatic cylinder, I'm thinking I can evolve the belt drive/PDB into one workable model and use a PDB lower anchor. Just need to find the time to modify the models I have. Thinking at this time, the TTS system is losing favor.

Comparing the CatR8 drawbar model with the patents from the Mach 1 information, they are very similar. I'll scrub through them both in the near future to try to come up with something that will fit my application. May have to purchase some pull studs from Mach 1 to get to the perfect fit needed.

Going to ISO30 would require a new spindle. I'd still need to make my own drawbar I think. Thinking I can make it happen for less than the price of it and all new tool holders. Guess it does solve the pull stud issue though or I'm guessing that what the 1/2-13 threads are for. But not sure after reading this "The NMTB shank was developed for use in the NMTB spindle which uses a draw bar to pull the shank up into the spindle. As a result, the tool flange thickness and the distance from the gage line of the taper to the outward face of the flange was not a critical dimension and was not consistent between all manufacturers of NMTB tooling."

So, what do ISO30 tool holders give me that R8 won't? Larger taper which is good, but beyond that I don't get it I guess.
Bob

**RustedOut** · 12-01-2011, 01:42 PM

I've continued to study other smaller commercial mills and found a write up on a Hass Mini Mill that says the belt drive is a 1:1 drive that runs up to 6000 rpm. It uses a 7.5 hp motor, so has a boat load of torque, but with those numbers the over speeding of the motor has to be how they got there. A 7.5 hp motor going 6000 rpm, wow!

So basically, their doing the same thing I intend to do. However, I've gone back to the 2 hp inverter motor with a lot less torque than their 7.5 hp. Still leaning toward the single ratio pulley set up to see what results I get. I'll leave enough room to add another pulley ratio stacked on top of the first in case I need to go there.

Decided on doing the internal splines with a single 6mm broach and a custom bushing that allows me to lock in the 60 degree rotation between the splines and cut them individually. I'll wait till after Christmas and New Years now to purchase the broach. Same with the VFD and pulleys. Got the money for all of it, just not wanting to turn loose of it right now. Most everything else is already in the shop. I have some welding jobs in the shop right now, but when those are done I may start turning the hub and milling the new top plate and motor plate. I'll post up some photos when I get to that stage.

Bob

**BobWarfield** · 12-03-2011, 01:43 AM

Originally Posted by RustedOut

I've continued to study other smaller commercial mills and found a write up on a Hass Mini Mill that says the belt drive is a 1:1 drive that runs up to 6000 rpm. It uses a 7.5 hp motor, so has a boat load of torque, but with those numbers the over speeding of the motor has to be how they got there. A 7.5 hp motor going 6000 rpm, wow!

So basically, their doing the same thing I intend to do. However, I've gone back to the 2 hp inverter motor with a lot less torque than their 7.5 hp. Still leaning toward the single ratio pulley set up to see what results I get. I'll leave enough room to add another pulley ratio stacked on top of the first in case I need to go there.

Decided on doing the internal splines with a single 6mm broach and a custom bushing that allows me to lock in the 60 degree rotation between the splines and cut them individually. I'll wait till after Christmas and New Years now to purchase the broach. Same with the VFD and pulleys. Got the money for all of it, just not wanting to turn loose of it right now. Most everything else is already in the shop. I have some welding jobs in the shop right now, but when those are done I may start turning the hub and milling the new top plate and motor plate. I'll post up some photos when I get to that stage.

Bob

Bob, before you take the Haas path, I wanted to pass along some info. I've had 2 Haas users so far that had terrible spindle stalling problems. It resulted in my adding horsepower curve compensation to G-Wizard. It is really pretty amazing how much the power drops off on that Haas spindle at any kind of speed. See this article about it:

Taming an Unruly Spindle Power Curve With G-Wizard « CNCCookbook

Now that's with a big honkin' 7.5 HP motor and a nice vector drive--not cheap. Yet, you've only got 2.5 HP left when you're at 6000 trying to do aluminum. No wonder those guys were stalling their spindles!

I'd definitely go for 2 pulley ratios on a belt drive like this. Makes a huge difference. If you've got money to burn, I'd look at a 5 HP motor too. This mill will take that. Certainly a 3 HP.

Cheers,

BW

**RustedOut** · 12-03-2011, 05:31 PM

Thanks for that great info Bob. I usually follow your web site pretty close, but hadn't been there in a number of weeks so I missed that. That looks like a very nice addition to your already fine GW package. Been thinking I need to finally invest in it, but just not had the loose cash for it yet. I really liked the beta versions. Maybe I need to make that investment before I start making parts for the belt drive conversion.

I began having some doubts a couple months ago about the performance of the 1:1 single ratio setup I mentioned earlier at lower rpm's. Especially after some private conversations with some pro's in the motion engineering business and my thinking of using a 2 hp motor instead of the 3 hp. Convinced myself the 3 hp motor I have is just too heavy at 98 lbs. The 2 hp is half that, but torque, like the hp, is a third less as well. Never really thought about loss of hp at the higher range though. But I am now thanks to your post. I don't generally run those aggressive cuts like you illustrated though, but it does give me something more to think about. What's your thoughts on the weight of the larger motor on an IH mill? I guess I could stack some weight on the mill head and run it to see how it performs. I believe it's about 30 to 40 lbs more than what it is currently with the gear drive and stock IH motor. I've forgotten the actual difference. It may be as low as 20 lbs more.

My doubts, mentioned above, lead me to explore a back gear in addition to the single ratio belt drive. I liked where it was going, but I'm not sure if I'm currently a good enough machinist to manufacture some parts of it, namely the dog clutch and tolerances involved in it. So some real doubts there as to the feasibility of it in my case. Can't say I've abandoned it altogether, but it's stalled at about 65% design completion. It would allow a 4:1 reduction in addition to what ever belt drive ratio I choose. A two ratio pulley setup would be a lot easier, not that I'm into easy, but I'm not that much into complicated either. Cost either way should be a wash, but time wise, the pulley setup requires less. Problem is I believe the back gear option is a better solution than the multi pulley setup in low rpm operation with the 2 hp motor. It has rpm limitations though when engaged. Most likely I'd go with two pulley ratios if the 3 hp motor is driving it.

Seems like I'm flip flopping on which direction I need to go because I am.

My decision to push back the start of the build until the first of the year gives me a little more time to ponder which direction works best for me. I only want to do this once, but with a two ratio pulley setup I could correct things to a point later on if needed. I'm leaning, for now, toward the 2 hp motor, but I can make either one fit. Early decisions were based on the larger motor, but with it possibly out of the picture, some things will have to change. Your input here may push me back to the larger motor.

Sorry for the long post, I should learn shorthand. And thanks for the input, advise from you guys is why I share where I'm at with this project. I'm certainly no machine designer and need all the help I can get.

Bob

**BobWarfield** · 12-03-2011, 05:49 PM

Bob, about the only thing I would think a back gear would buy you is big twist drills might be happier in steel at the lowest rpms. Can't think of much else that eats the horsepower at such slow speeds.

Unless you have reason to believe that will be commonplace for you, I wouldn't agonize too much on the back gear. You can always interpolate the hole and I would think a 3 HP can run a 1" twist drill just fine with a vector drive.

If you're just trying to avoid pulley swaps, I would either focus on making swinging the motor to get slack super easy or look at the Fadal-style idler pulley "gear change" for 2 pulley setups. I have some discussion and pix of it on my site:

CNC Cookbook: Mill Belt Drive, Pt 1

I'd start out with a couple of cam locks rather than the air cylinders for simplicity, but even going whole hog can't he all that hard.

I'm gearing up to machine my pulley setup over the Christmas holidays. Got access to a friends Romi CNC toolroom lathe, which is a real nice machine and much larger than my dinky lathe. Just ordered 2 slugs of 6" diameter 6061 to do the work. I'm going to make my pulley diameters quite a bit larger than a lot of the belt drives I see on the 'Zone. Supposed to be helpful transmitting the power. I came across some Gates design handbooks that suggest a minimum size for various HP levels and with 2:1 or 1:2 ratios, it suggests a little larger pulleys than most of the ones we see.

RE the motor weight on the head, those RF45 heads are heavy, however, there are some mitigating factors:

- You can clear out the contents of the gear box with a belt drive. In all honesty I would personally be tempted to fill it back up with epoxy granite, so that may not be a savings for you.

- You can run a different servo to ballscrew ratio on the Z axis so you have more grunt. Mine is a different ratio, don't remember exactly what the two are any more.

- You can stick a larger motor on Z. Again, mine is larger. I have the over 1000 sized homeshopcnc on Z and the 850's on X and Y.

- You can counterweight the Z. Gas shocks are especially nice and not very expensive.

I haven't had much trouble with Z. It benefits greatly with a one shot oiler, and if I forget to pull the lever often enough Z is usually what faults.

One quasi-bummer: Mach3 has a real problem if the axes have different acceleration rates. I started out tuning each axis for its fastest acceleration and all sorts of weird stuff was happening to the parts. I finally had to dial back to the Z accel rate, as it was the lowest of the 3 and set everyone to the same rate. HimyKibbible put me onto that I think.

It's possible this was fixed, I haven't upgraded my Mach3 in quite a while.

I guess the ultimate Z mod would be to machine the dovetail off an go to linear rails. That'd be sweet, and ultimately not that difficult. I seem to recall Cruiser put together some kind of hybrid that added a linear so the head would "nod" less. I'd love to try that someday, but it is a LONG ways down my list of priorities!

Cheers,

BW

**RustedOut** · 12-03-2011, 08:31 PM