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IndustryArena Forum > MetalWorking Machines > Benchtop Machines > RF-45 Clone Mill > Questions on bearings for Belt Drive Conversion
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  1. #1
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    Questions on bearings for Belt Drive Conversion

    Howdy,

    I've worked up a Belt Drive conversion in SolidWorks for my (inherited) IH mill, that has never been turned on.**

    So should the bearing in the new top be angular contact? The old ones just read 6002 nothing else. Undoubtedly very cheap bearings no doubt.
    Another thing is the spindle feels a little rough at the bottom when I turn it by hand, like the bearing has grit in it or something. Not sure what it is. I'm thinking of replacing the lower bearing with something a lot better.

    Don't quite understand the preload thing. If you buy the bearings do you preload them yourself as you put them in. If so how? I don't mind spending on good quality bearings, just not way too much - like I don't want to spend $750 per bearing or anything like that.



    *** The Belt drive will use a Baldor VM3561T 3hp 3 ph. with a Hitachi vector drive, 2:1 poly-v pulleys

  2. #2
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    Re: Questions on bearings for Belt Drive Conversion

    I made the belt drive you have.

    You have spindle bearings and the belt drive has bearings. The drawing you show is of the belt drive but your talking about the spindle bearings.

    I don't have all the bearing # in hand but all the RF-45 clones have tapered roller bearings in the spindle. All are China bearings but if they are not full of rust should be OK to about 5000 RPM if you re pack them with a good grease and set the preload slightly low. Standard grease is a bit too thin and will melt out. I would have to look up the proper grease #.

    Most the belt drives I made have a higher top speed with a VFD motor at 100 hz. Generly 6.5K with a 1750 RPM motor. If you plan on running over lets say 4K all the time then its a good idea to change to A\C bearings.

    Its not really all that easy to change them and get the preload set correctly. You set the preload with the two spanner nuts at the top. The problem is the top bearing generally will not slide easily on the shaft so will stick slip as you set the preload. This makes using a soft blow hammer useful in setting the preload just right. Any made in Japan A\C standard grade bearing is just fine. I got about .0003" of runout from one.
    youtube videos of the G0704 under the name arizonavideo99

  3. #3
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    Re: Questions on bearings for Belt Drive Conversion

    Quote Originally Posted by arizonavideo View Post
    ......I don't have all the bearing # in hand but all the RF-45 clones have tapered roller bearings in the spindle. All are China bearings but if they are not full of rust should be OK to about 5000 RPM if you re pack them with a good grease and set the preload slightly low. Standard grease is a bit too thin and will melt out. I would have to look up the proper grease #...... If you plan on running over lets say 4K all the time then its a good idea to change to A\C bearings.

    Its not really all that easy to change them and get the preload set correctly. You set the preload with the two spanner nuts at the top. The problem is the top bearing generally will not slide easily on the shaft so will stick slip as you set the preload. This makes using a soft blow hammer useful in setting the preload just right. Any made in Japan A\C standard grade bearing is just fine. I got about .0003" of runout from one.
    Thanks for the reply! I tend to do a fair amount of work at around 4000 rpms. Small holes and such. I do model engineering, so the work is rather small as one can imagine. Is Kluber the right grease ?
    As far as setting the preload, how do you know when you have it right? Do you keep adjusting the spanner nuts until you reach a minimum runout or what?

    I'm finding that upon removing everything: mill top w/ gears, quill feed spring, quil downfeed shaft, quill stop etc. etc. the spindle only drops down about 9 inches. Should come all the way out I should think. Something seem to be holding up. and won't go any further; gave it a couple of light whacks with a dead blow but nothing doing. Any idea what it could be?





    Thanks in advance!

  4. #4
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    Re: Questions on bearings for Belt Drive Conversion

    Kluber should be fine.

    4K is OK with stock bearing but you do want to use better grease and make sure everything is clean. You can wash out everything in solvent and grease it when its together. The bottom bearing cover is not a seal just a dust cover.

    Now on setting preload.

    When new all the TRB make a lot of heat but still should turn smooth. They are really, really strong bearings, much stronger than A\C bearing but they don't like going real fast.

    For high speeds they will need to break in and have light preload. This is a fussy process because they run almost dry. If you have just greased them the grease layer will be thicker than in real life so the preload will get looser after a few hours.

    Break in needs to be around 10 hours of use. Fine preload adjustments can be made by smacking the splined top of the shaft to loosen the preload ever so slightly or a tap on the R-8 end to make sure its tight. Cover the shaft with a soft piece of aluminum plate. I made spanner wrenches but a lot of things might work to adjust the nut. Were talking about rotating the lock nut less than the thickness of a quarter from too tight to too lose, like 1-80th of a rotation. Making a mark on the shaft can help you see if you rotated the nut ever so little. A sharpie mark on the nut and shaft is a good idea.

    The fit of the top bearing on the spindle shaft is often a light press so rotating the two nuts may or may not change the preload. If you take it all the way apart then use some 500 grit to clean up the top part of shaft where the bearing runs. It will make setting the preload easier if the bearing fit is not so darn tight. Don't make it fit loose just no so darn hard.

    If you set the preload so it turns lets say two or three times if you spin it by hand than that might be close. The real test is how much heat it makes.

    Run it for a short time like two minuets and check if the lower bearing is hot. If its smoking hot you need to lower the preload before running it more. If its cold then run it for 5 min in high and see what you have. It should be warm.

    A properly broken in spindle with TRB and good grease at 3K will run fairly hot. If you run it for 20 min and you can't hold you hand on the lower bearing then its too tight. If its only warm it might be a little loose. It should be about as hot a a cup of coffee after a hour of running. You don't have gears anymore so the head will run cool except for the spindle.

    If you get it right and add some grease a few times a year the bearing will last many years. The bottom dust cover is not a seal and if you blow off your work with air you will blow crap into your bearing. I made a rubber seal but it cant rub the shaft almost at all or it will get hot and melt.

    All in all you can do this in about two hours time.

    The spindle is retained by TWO set screws on the left side and the quill rack and return spring have to be removed.

    Be careful of the spring. You have to remove the little philips head screw on the shaft and rotate the spring to get it off.

    Let me know how it goes.

    Getting the belt drive to run quiet is a bit fussy too but that is for a different day.
    youtube videos of the G0704 under the name arizonavideo99

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    Re: Questions on bearings for Belt Drive Conversion

    Quote Originally Posted by arizonavideo View Post

    The spindle is retained by TWO set screws on the left side and the quill rack and return spring have to be removed.

    Be careful of the spring. You have to remove the little philips head screw on the shaft and rotate the spring to get it off.

    Let me know how it goes.

    Getting the belt drive to run quiet is a bit fussy too but that is for a different day.
    I found the little screw for the return spring --- the return spring actually has a keyhole shaped end that engages a small Philips screw
    set into the quill feed shaft --- had to pull out on the spring gently just a little while rotating the spring somewhat back and forth in either direction till I finally discovered/saw the little Philips....weird.

    Well I've have the spindle/quill pulled now...the so-called dustcover for the lower bearing has three small screw holes so it looks I'll have to make some sort of a simple "puller" based on these three threaded holes; perhaps that dust cover is lightly pressed in....I don't know...but I can't get a hold of it with any ordinary run-of-the-mill tools, let alone my fingers. But we are getting closer !!!

    Really, the more I think about it....the time that is invested into looking into the potential issues with the bearings reminds me that perhaps I should is dispense with them and at least get good quality angular contacts....I'm already in elbow deep. And the lower one: to me -- does feel gritty or rough "something definitely ain't right" .. based on other machines I have used in the past.

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    Re: Questions on bearings for Belt Drive Conversion

    Its a fair amount of work changing them and you will need a few cups and sleeves to press them on. A\C bearings are a bit shorter too so you might have to use a spacer under the lock nut. You might run out of threads.

    I have done a few so far and one had short threads.
    youtube videos of the G0704 under the name arizonavideo99

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    Re: Questions on bearings for Belt Drive Conversion

    On my spindle, the so called dust cover is threaded, and the three "holes" are just dimples made with a drill. I loosened it with a few gentle
    taps with a punch.
    Got mid priced SKF AC bearings on the way, and will make some kind of seal, if I can't fit a conventional rotary seal.

  8. #8
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    Quote Originally Posted by Zeroviz View Post
    ...
    Got mid priced SKF AC bearings on the way, and will make some kind of seal, if I can't fit a conventional rotary seal.
    Which SKF bearings did you choose?
    On my spindle that same "dust seal" was threaded like yours but so poorly you could almost spin it off with your hands!

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    Re: Questions on bearings for Belt Drive Conversion

    SKF 7206BEP, and SKF 7207BEP. A little hard to tell from SKF website data, but more or less equivalent to ABEC 5 ( P5, P6) with limit speed of 13,000 and 11,000.
    There are few versions, I just went with what I could get online.

    The thread on mine is pretty good. The TRB' s were easy enough to remove, especially if you've ever changed out motorcycle headset bearings, but I have taken note that it might be a good idea to make sure the upper AC bearing is more of a sliding fit, to make preloading them easier

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    Re: Questions on bearings for Belt Drive Conversion

    Arizonavideo,
    Thanks for all your help! I think what I will do is replace the TRBs with fairly decent quality TRBs of the same type, size. The chinese in my opinion can never be trusted: good example of this is when I took apart my Z axis then removed the acme nut, a broken drill bit was serving as the taper pin to hold in place!! While we are at it, when I took apart the head to remove all the gears, the head had foundry sand in it!
    So I can imagine if the inside of the quill and consequently the TRBs have all manner of debris casting slag or foundry sand in them. Shouldn't be at all surprising. Thus in order to see that everything is clean and in order I'll take out the so-called factory bearings, clean everything out and replace with new Japanese Nachi TRBs of the same size 30207 30206 (from VBX). Does this sound like a reasonably good plan? Is there anything I need to watch out for if replacing same bearing with same bearing? Does the fit of the inner bore of the TRBs need to be slip sliding fit or light press fit. How should the replacement outer races need to fit into the bores? What if the outer races are too loose or too tight? I ask because the cheap bearings that came with mill might differ in size from the Nachi's. Maybe - maybe not.

    Thanks!

  11. #11
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    Re: Questions on bearings for Belt Drive Conversion

    For the lower bearing if your going to do the work just go to AC bearings.

    Any Japan bearing will be fine. Standard grade. I got .0003" run out from a 20 year old USA bearing and .0004" from a new Japan bearing on a different spindle.

    The lower bearing need to be pressed on with a light press fit for the inner race. You can put the spindle in the freezer and use a long pipe that only hits the inner race and it will tap on real easy. Put the spindle on a soft surface so you dont dent it like a hard plastic or soft aluminum.

    On the lower bearing outer race it is driven out using a pin driver. There is two holes in the lower spindle to this. Clean the surface look close for burrs. It is with a green pad and get it 100% clean. A press would really help here because the race will want to rock and make a burr and then not sear properly.

    Again freeze the race and worm the housing will make it go in easy. You can put the housing in the oven to 200 deg if you like.

    I made a driver on the Lathe to fit the race. You will need to find something to drive it in. If you can add a long shaft to the drive it will help for you to see if it is straight.

    On the small bearing you can leave the stock one in or replace it with a new one or go to a AC. The biggest problem setting preload is the top bearing sticking to the shaft and then slipping and being too tight or loose.

    See how tight yours fits. Give the shaft some ever so light sanding with 500 grit or finer sand paper with the shaft spinning to make it even so it only takes a light force to get the bearing to move. It needs to be tight or you will get slop but getting the preload set is the most important thing.

    The top stock TRB is much smaller and can do 6K or 8K just fine. It is also a bit taller than the AC so might make it so you don't have to make or order a shim to set the lock nut.

    If you need a shim look at Mcmasters. They have some.

    Hope that helps
    Dave
    youtube videos of the G0704 under the name arizonavideo99

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