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IndustryArena Forum > MetalWorking Machines > Charter Oak Automation Support Forum > How well do the belt drive conversions work when milling steel?
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  1. #1
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    How well do the belt drive conversions work when milling steel?

    Currently doing some upgrades to my IH mill, moving to a ethernet Smooth Stepper and a break out board with more inputs. I’ve already built a fairly nice console using modbus and hard switches and I have to say it’s awesome. I should have built it years ago. One other improvement I did sometime back was to go with a solid state hard drive along with about twice the memory my previous pc had and a video card with it’s own memory.

    I’ve just finished bench testing the new electronics this week and planning on having the mill back up and running next week. Next on the list of upgrades is a new spindle. I have an R8 now and bought an ntmb30 and am going to make a new spindle housing to use 2 angular contact bearing at the lower end and get away from the single tapered roller there. Upper will be a deep groove ball bearing. I'd like to rework the spindle to accept a BT30 gripper, but if I need to, I’m prepared to run a threaded draw bar for a while so I can use my collection of BT30 tool holders and pre-setter.

    I have a 3 phase motor for the spindle that I’d planned on adding, the vfd for it is in the cabinet now. And regardless of which way I go, there will be a new spindle motor up there in the near future. Originally I had planned on going with the 2 position belt drive solution so many of you guys have done and in the past I got into some discussions on them. Then I started liking a single position belt drive and over speeding the motor some to get the higher rpm. In that case, the pulleys would be a reduction to increase the motors torque.

    But for the past two years or more, I’ve found myself milling more steel that anything else. And that has stalled out my desire for the belt drive. A close second has been acetal, then aluminum. Lots of the steel is tool steel that ends up getting heat treated, so the need for a higher spindle rpm just hasn’t been there. But I will admit the stock 1600 rpm is a bit slow lots of times even in steel. The higher spindle rpm is the main thing that the belt drives gives the mill, but once converted, the original gears are gone. So there’s a huge loss of torque.

    I’ve not done much thinking of just what the gear ratios in the standard mill head are, but I know they are steep in some cases. I know that the increased torque from the gearing can be replicated by more horse power. The commercial mills I've checked out have that larger horse power nowadays and I know they work well in either media. But most of those start at 7.5 hp and go way up from that. So they start with lots more torque than the 3 hp 4 pole motor I have on hand. If my thinking is correct, HAAS uses a 1:1 pulley ratio and runs only one set of pulleys (but way more horse power).

    So I got a question for you guys that have made that conversion. How does your belt drives do when cutting steel? Do you have to take smaller doc’s and step overs to be able to run them vs when you had the stock gearing? I'm believing most of you used either a 2 hp or 3 hp motor, do you find that adequate with the belt drives you've done? What would you do differently if you were to do it all over? I don't see my machining projects changing much if any for the next couple of years at least, so I need to make changes that help me do what I do. Not hinder me. I want the cnc programs to take control of the spindle and that mostly means I should get rid of the gears. But I'm a bit afraid to. I'm ok with changing my machining tactics if things will work well enough, but there's not that much a guy can change when he's drilling a 1/2" or larger hole in steel. I got no worries on lots of the lighter stuff I do and running smaller end mills, the boring head, fly cutter and even the face mill, but I do with those that seem to me to require quite a bit of torque.

    Thanks in advance for your input
    Bob

  2. #2
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    Re: How well do the belt drive conversions work when milling steel?

    well a 1/2 dia hole in some tool steel should take about 1/2 hp to drill and you should be able to run at 300-350 rpm. now depending on your vfd you may or may not have full torque at the low rpm of the frequency range and you'll have to check that. ideally your motor should run at 50/60hz at 500 rpm. when I was doing my calculations for the hp, it made more sense to use a 1500 rpm motor and over speed it vs a 3400 rpm motor and try and run it slowly, due to the torque penalty. but with a belt drive I don't think you'll have any problems.

  3. #3
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    Re: How well do the belt drive conversions work when milling steel?

    I cut a trunnion-type fixture out of a 2" bar of 4140 with a 1/2" FEM a while back. My machinist buddies were dumbfounded that this was possible. I won't say it was fast, but it did the job. I've been running one of Daves two-speed belt drives for several years now and I can honestly say that I would have dump the whole mill if not for this upgrade. One of my friends with a Haas TM-2p came over and couldn't even tell the machine was running/cutting until he was right next to it. I'm still running the tapered roller bearings and don't hesitate to engrave at 5800 rpm. I keep saying I'll swap to the angular contacts when these give up, but they just won't die. I also fabricated some o-ringed plugs and machined the quill to accept a grease seal so I can run oil in the lower bearing, but it's been so happy with Kluber spindle grease that I haven't ever put oil in it.

    I highly recommend the two speed belt drive as I definitely drop down to the low ratio for speeds under 1krpm. I also tend to run higher rpm/smaller diameter tool combos to avoid rigidity and HP issues. Attachment 312010

  4. #4
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    Re: How well do the belt drive conversions work when milling steel?

    Quote Originally Posted by Runner4404spd View Post
    well a 1/2 dia hole in some tool steel should take about 1/2 hp to drill and you should be able to run at 300-350 rpm. now depending on your vfd you may or may not have full torque at the low rpm of the frequency range and you'll have to check that. ideally your motor should run at 50/60hz at 500 rpm. when I was doing my calculations for the hp, it made more sense to use a 1500 rpm motor and over speed it vs a 3400 rpm motor and try and run it slowly, due to the torque penalty. but with a belt drive I don't think you'll have any problems.
    Yeah, but that 1/2hp motor is going to be seriously gear reduced. At least my drill press is and my 1/2hp hand drill is as well. The drill press needs it just to get to that rpm, but it helps a lot on the torque.

    My electronic upgrade has been in work far too long, but the breakout board is not being nice to me. Everything else is working but it and it's part time. So I actually got a chance to mess around with the spindle motor I intend to use. It's not on the mill, but in a fixture. It's 3 hp and got quite a bit of torque to it. I can run it down to right at 300 rpm at the spindle which would be 540 on the motor shaft and have full torque. I could actually go slower than that, but it seems a good low end until I can actually get it in use and see how things work. Those numbers end up with 18 hz from the vfd. This is an 1800 4 pole, 1735 base rpm motor. The vfd states it yields full torque down to 10 hz.

    Quote Originally Posted by ksanalytical View Post
    I cut a trunnion-type fixture out of a 2" bar of 4140 with a 1/2" FEM a while back. My machinist buddies were dumbfounded that this was possible. I won't say it was fast, but it did the job. I've been running one of Daves two-speed belt drives for several years now and I can honestly say that I would have dump the whole mill if not for this upgrade. One of my friends with a Haas TM-2p came over and couldn't even tell the machine was running/cutting until he was right next to it. I'm still running the tapered roller bearings and don't hesitate to engrave at 5800 rpm. I keep saying I'll swap to the angular contacts when these give up, but they just won't die. I also fabricated some o-ringed plugs and machined the quill to accept a grease seal so I can run oil in the lower bearing, but it's been so happy with Kluber spindle grease that I haven't ever put oil in it.

    I highly recommend the two speed belt drive as I definitely drop down to the low ratio for speeds under 1krpm. I also tend to run higher rpm/smaller diameter tool combos to avoid rigidity and HP issues.
    4140 PH is a steel I cut a lot, D2 and 01 being some others. And I use quite a bit of inserted end mills doing it, up to 1" in diameter. I don't really care about this mill being screaming fast, just somewhat faster than what it is. Quiet would be higher on the list though and I have noticed the new motor is real quiet, even with the flat paddle fan it has. While I've been working on the electronics, I've given a lot of thought to the next step and have decided to go with the 2 belt solution. That keeps the motor running at the noted 18 hz and up to 112 hz. Yields 300 rpm in low and up to 6000 in high with some overlap in the 1200 to 2000 rpm range.

    I did order the angular contact bearings the other day, putting in two in the lower end in a back to back configuration. The stock IH housing won't accommodate them though, so I'm making a new spindle housing. I sure thought I had read that some guys had done that swap and didn't recall them making a new housing. Maybe they reworked it, just don't recall now. You mention running oil in them. I was wondering about that, but I think I've come to the decision to just go with grease. I designed the new housing like Bridgeport did theirs so it is a light press with the lower bearings being fixed by a screw in ring/labyrinth seal and a lock screw. It'll have a spacer between the lower two and the top single bearing. That way I can just press the spindle and bearings out and regrease them as needed. So lots of thinking lately with very little action.

    Thanks for the replies,
    Bob

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    Re: How well do the belt drive conversions work when milling steel?

    Wow, I'm slow. But i now have a BT30 spindle in the mill running with 2 AC bearings at the bottom and one deep groove ball at the top. I made the new housing from cast iron. It was in my lathe forever it seemed. A good part of the working time was in getting the hole clear through so I could start to turn the bearing surfaces. Had to work from each end in my 20" long lathe.

    Starting out, I didn't have a good way to measure the bores for the bearings outside of a set of telescoping gauges. I didn't like that option, so I spent some time figuring out what to get to do that task. I had never even held a bore gauge in my hand before, but I ended up buying a set that gets me from under an inch to over 6 inches all with .0001" resolution. Then of course I needed the bearings and they weren't at give away prices. So on a retirement budget, these items took quite some time to get in hand.

    I also don't own a surface grinder and one of my parts required that. Most of the machine shops around me have the word aerospace in their names, and that usually means they are pretty expensive if they even think they want to mess with my little one time stuff. So finding a shop that was willing to work with me and not break my bank took some time as well. The housing spent about 3 months in the lathe before I got it finished, started in late April. But it came out in tolerance and looking very nice, if I do say so myself.

    I pressed the bearings on the spindle a couple days ago and then got that pressed in the housing the same day. Today I finished my draw bar and now have a working spindle again. With the pre setter, I'm anxious to get back to using the mill. It has been going through upgrades along with the new spindle and I haven't ran the mill at all outside of testing since february. A little more wiring to re-route and the way lube lines to hook back up and I should be back up and running. I'll have to check and correct the nod of the column and retram it now too. Adding the extra bearing at the lower end and using a NMTB spindle with BT30 tool holders, I think I lost about 1" in Z. For what I gained, that's a cheap price to pay.

    Attachment 327636

  6. #6
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    Re: How well do the belt drive conversions work when milling steel?

    amazing work.

  7. #7
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    Re: How well do the belt drive conversions work when milling steel?

    Thanks Runner,

    I've been running it even without the new chip enclosure being completed and having a few cables clamped up out of the way. Things were piling up on me. Right now I don't have the rpm to even break in the new bearings properly, but I think they'll be fine when I do. I've got a few more BT30 tools to acquire before I can mill the new top plate for the mill head so I can get the belt drive installed.

    Bob

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    Re: How well do the belt drive conversions work when milling steel?

    "How does your belt drives do when cutting steel? Do you have to take smaller doc’s and step overs to be able to run them vs when you had the stock gearing? I'm believing most of you used either a 2 hp or 3 hp motor, do you find that adequate with the belt drives you've done?"

    With a single speed belt drive that was .9 to 1 underdriven and a 3HP 3650 motor it worked well for most everything with only a problem driving large taps and drilling 3/4" holes.

    One option I thought of was to just go to a 4HP motor and a 5 HP VFD and go direct drive. It would be simple but you have to deal with the draw bar and quill movement


    The two speed belt drive really has no problems at any speed and works well with a 2 hp motor.

    I still have a single speed belt drive sitting here. Its extra.

    Someday I would like to have a system for all the RF style mills.
    youtube videos of the G0704 under the name arizonavideo99

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    Re: How well do the belt drive conversions work when milling steel?

    For perspective, I had a error in my gear ratios in Mach3 when I machined that 4140 trunnion. The result was that I was actually cutting 0.25 deep (I believe that was the doc) at 0.011" chipload (HSM toolpath). You'll run out of rigidity way before you run out of HP for milling.

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    Re: How well do the belt drive conversions work when milling steel?

    After lots of thought and feet dragging, I've pretty much convinced myself to go the two speed belt route. I've tried to make the case that I could have both belts in place all the time with one or the other tensioned. But i'm pretty much scared of that for now. So I'll be swapping a single belt to either position. My pulleys are 1.8:1 and .555:1 (I think I stated that right). I've already worked out the minimum and maximum speeds for each position in Mach3 and have tested my motor. It's a 3hp Baldor, but a 1800 rpm base. So that puts the top motor rpm at 3334 with my max spindle speed in either position. I actually recall it being lower for the slow speed position. I've run the motor on the floor for many hours now and it seems to do well. Actually, I've test run both the 3hp motors on a test stand up to over 11,000 rpm with the only apparent ill effect being the noise of the flat paddle fan. Taking that off, the motors just sit there and hum right along. And don't even look like they're running at all. They weren't driving anything though.

    I don't have a quill any longer, it's been gone a long time. That helped with the making of the new spindle housing. Your numbers on the larger tap and drills is where my thinking has been on the subject. I don't plan on tapping anything larger than 1/2" or drilling much more than 5/8". Anything more than those, I'll do with an end mill in the case of holes. If required, I'll use a boring head after milling them. And I want to get to thread milling at some point.

    I've gone to a threaded draw bar instead of using pull studs and a gripper even though I have already built a gripper. I decided to not modify the spindle to accept it. My plan is to design and build an all electric auto draw bar. I'll get the mounting points worked out soon and start on the new top plate for the mill head, then get to work on the auto draw bar once I have the belt drive installed.

    That brings me to another question though, I'm assuming most of these conversions are using micro-v belts. That's what I made my pulleys to fit. Does it take extreme belt tension to avoid belt slippage? I have them on two smaller machines I've built and have actually locked them up without any discernible slippage of the belt, but they are 1 and 1 1/2hp machines. They aren't mills, but drive a ram up and down. My belt tightening system on the mill is going to be a spring loaded arm with an idler roller applying the tension.

    You mention a 4 hp motor, that has to be fairly heavy. I know you've been messing with the drive systems on these for a while. How well would a normal IH mill handle the extra weight of that big of a motor. I have a 100 lb 3 hp motor that I decided not to use in favor of a 76 lb 3 hp motor because I was concerned with the servo motor dealing with that kind of weight. But I don't know what weight will be coming out in the gears and bearings. Both motors have very similar performance, so I'm not losing anything but weight I think. I know my mill could handle more weight there, just not sure how much more. But I have a 5 hp 1800 rpm motor and it weighs less than the 76 lb 3 hp does, so it's likely a 4 hp could be close in weight. But I've always considered that 5 hp overkill for my mill. Those are all actual scale weights, not their listed weights.


    Thanks for the advise,
    Bob

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    Re: How well do the belt drive conversions work when milling steel?

    Any more, I tend to error on the side of conservatism on feed and chip load. Broke too many cutters I guess. Don't think I ever had that heavy of chip load before though on a 1/2" end mill in steel.

    In creating my new tool library for my CAM, I want to get real world numbers in there so it can calculate the correct speeds and feeds. With the R8 tool holders I was running before, I was all over the place on cutters so I never had any hard numbers for them. That has been the biggest source of not getting things right in my programs. And I had things set up for aluminum at first, then got to doing more steel the last 3 years or so. I'll have two tool libraries when I'm done, one for aluminum and one for steel. Creating them has turned out to be a lot of work, but I believe it'll be worth the time in the end.

    You're right on the rigidity of the mill. I think 3 hp is about as much as I care to throw at it. I started out planning to run a 2 hp motor, but quickly upgraded my plan to the 3 hp size. My concern of less torque from a belt drive vs the geared head drove that. Going to be interesting to see how this works out.

    Bob

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    Re: How well do the belt drive conversions work when milling steel?

    " My concern of less torque from a belt drive vs the geared head"

    You have said a few times about the torque loss of a belt drive. I know you don't have quite the reduction that you get with the gears but the reduction in low range is about 2.3 to 1.

    With a 3 hp motor you will never stall the mill if the VFD is set up properly with its RPM compensation set to a good level.

    I do have a extra 10 groove pulley that I could let go for cheep. I have changed the offset that I used to allow for the last grove to be thicker so this one is a bit thin.

    It is the motor pulley for a 1750 motor and is cut to accept a QC bushing. You do need a long shaft motor. For the short shaft IH motors I make the motor pulleys taller.

    I'm to busy right now to do any more belt drives but I mostly do all 8 groove pulleys anymore so I don't need this one.

    Dave
    youtube videos of the G0704 under the name arizonavideo99

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