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IndustryArena Forum > MetalWorking Machines > Tree > Converting a 325 from 3.5k to 6k RPM
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  1. #1
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    Converting a 325 from 3.5k to 6k RPM

    I just got done doing up my mill to go faster and thought I'd just drop a thread to help others. My mill is a 325J. It has the 3500RPM spindle, with the Yaskawa spindle motor and formerly yaskawa drive (swapped it out for a Teco MA7200 last summer when the Yaskawa poo'd the bed). The mill was in near mint condition when I got it and spent most of it's life cutting plastic so I kind of lucked out. Spindle bearings are good as was just about everything else.

    Parts required are:
    5.2" 8L taperlock Pulley
    Appropriate Taper lock Bushing
    63.5" 8L Belt (635L8
    New 8mm key for the pulley (mine was 8mm YMMV)
    Maybe new Precision Matched bearings for the spindle pulley.
    a short jumper wire
    Possibly a torch
    Possibly a bolt type wheel puller
    Some soap for your mouth so that when its done you can feel better about kissing your wife or mom

    Getting it done:

    So first you need make with ordering the parts. I got this pulley. Note that the screws are British Whitworth. This doesn't really matter as long as you don't lose the screws, which do come with it. And don't let the 10 groove scare you away. The pulley is an L pitch so you will just have 2 unused grooves, the distance/pitch between the V's is the same. Big whoop. The thing is, this is probably the only pulley readily available to make this happen otherwise it is a 10-16 week wait for them to make one (in china by the way, not too happy about this but beggars can't be choosers). Next you will need the appropriate taper lock bushing. This is the one I got. The spindle on my motor is 28mm and this bushing is also British Whitworth to match the pulley. I ordered on Wed and they parts showed up on friday. Very happy with that. For the belt I hit up amazon as it seemed like the best deal and the only place I could really find what I was looking for. I grabbed this one which is a 635L8. After that you might need a new Key for the motor. Mine was stepped. The motor shaft was an 8mm but the stock pulley was a 7mm. New pulley is an 8mm so I ran to the local ACE and grabbed a new 8mmx40mm key. I had to shave about 0.5mm off of it to make it fit though. I also was told that new pulley bearings will be needed for this. Since I am not very affluent at the moment, I am holding off until I can swing it. I can always run at lower speeds until the funds roll through to get some sweet new bearings. I am 90% sure the bearings that are in there are a precision matched set, but I am not 100% sure. But they work at 3500rpm for now so I can run there if need be.

    Once the parts show up, you need to get the belt off and the old pulley off of the motor. This was a problem for me. The factory motor pulley had a taper lock bushing as well. Normally you just remove the screws holding the taper lock bushing into the pulley and put them into the other holes in the bushing so it becomes self extracting. Well I did this and the old cast iron bushing was wedged in there too tight and all the flanges broke off. So the next morning I grabbed a map gas torch and a bolt type wheel puller. I also opted to get some 10.9 metric screws of the appropriate length to fasten to the 3 holes that were used to affix the taper bushing to the pulley. This seemed to work well. I heated the crap out of the pulley with the torch and slowly got it off with the puller a quarter turn at a time. Took the better part of 45min to get it done. So beware there. You have to hold the pulley assembly still. To do this I shoved an 8mm Allen wrench into the unused slot in the puller and got one of the better upper body work outs I have had in a long time. Also if you destroyed the bushing like I did, you might be able to get a replacement from Ametric, assuming you ever want to go back. Or you can just get a new pulley and bushing. To swap belts, you have to pull the shaft cover off the top of the mill, then remove the 4 M10 (I think thats what they are) socket caps so that you can get the 1" thick top plate off. There are 2 taper pins on either side as well. You can thread in a M6 bolt to use to pull the pins out, but the pins on mine were stuck so I had to do some very careful prying to dislodge the cap. Applying heat might help but could also fry some of the paint Its your mill act accordingly. Once the cap is off you can remove the belt. Also, if you have a lot of knocking noise coming from the top end when the mill is running, there is a way to fix that assuming it is not a bearing. There is a little urethane piece on the bottom of the spindle pulley that you can adjust, maybe that will help take up some of the slack. Mine was shot so I made a new one very craftily. But that is a whole different can of worms for another post. Once belts are swapped you will have to tweak the motor pulley height a little then you are done there. Just make sure you put the Key in the keyway or bad things will happen. I had a manual mill where some idiot did that and it wasn't fun to correct that. To get the RPM's to change you go into the control cabinet and on the bus look for a terminal marked 238. One side of the 238 terminal should be empty. Take a short jumper and go to the terminal for wire 200. This will get you the 24v input needed to change the max speed from 3500 to 6000. But I will say, bust out the voltmeter and verify that you have 24v there. Always be safe. On mine, the 200 wire terminal (there were actually 3 of them in a row) were right next to the 238 terminal so this was easy peasy. The relays that control the spindle on signal, the drawbar and a few other things all run off of the 24v supply if my memory serves. If you have a wire diagram this will aid immensely if you have a non-standard arrangement in your control cabinet. All that is left is to reassemble and check everything.

    To test, I got an inexpensive optical tachometer from HF. It was like $40 and it seems to work well. I measured the speeds on the before and the after. Before, at around 3350rpm I saw about a 13% difference in the programmed speed and the actual. The actual speed was 3842. It was a pretty consistent 13-14% from 800 rpm up to 3500. After the swap the swing was much less. At 2k it was at around 2042. At 5250 it was running at around 5428, so it is roughly a consistent 3-5% or so off. I can deal with that. Not like I will be tapping at those speeds. I think the variation is partly due to the Spindle Drive swap I did. I got the factory parameters for the old drive and plugged them into the new drive. I think that they might have done the 3500rpm machine's volt hertz curve a little different than the 6k, maybe? I don't know. I may play with the curve a little bit, but really 3-5% difference ain't gonna kill me. Most of the tapping I do is under 500rpm so an extra 25rpm will be easily comped with the tension compression tap holders I use. But it will be interesting to see how well it taps now with the larger pulley mass adding a bit of inertia. I had to adjust the accel and decel times on the drive as i had tuned them a bit for the 3500rpm so that I could get it up to speed and stopped as quickly as the drive would allow. With the bigger, heavier pulley and the higher spindle speeds it takes longer to get to speed and a bit longer to slow done. So the longer stop/braking time could effect tapping some. We shall see.

    Hope this helps those that are looking at going down this path. I had trouble getting all of the information for this swap and put if off for way too long. Can't wait to see what this does to the cycle times of the parts that are run on it.

  2. #2
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    Is your new motor 7200rpm? Because I run a 4.8" drive sheave and a 6.4 driven sheave with my 8000rpm spindle motor to get 6000rpm spindle, if we have the same setup you should be turning 6500rpm with a 5.2" sheave.

  3. #3
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    Quote Originally Posted by Redzilla View Post
    Is your new motor 7200rpm? Because I run a 4.8" drive sheave and a 6.4 driven sheave with my 8000rpm spindle motor to get 6000rpm spindle, if we have the same setup you should be turning 6500rpm with a 5.2" sheave.
    I made this pulley on my little 12x36 lathe just to see if I could and it turned out really nice.

  4. #4
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    Re: Converting a 325 from 3.5k to 6k RPM

    Is your 6000rpm 325 still working well? Happy with it?

  5. #5
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    Re: Converting a 325 from 3.5k to 6k RPM

    Quote Originally Posted by pianoman8t8 View Post
    Is your 6000rpm 325 still working well? Happy with it?
    I love it. The belt speed is a bit high for my taste and it makes some noise because of it, but overall its great. Still has plenty of torque for what I do and I have to run it freaking hard to get it to slow. Have had no issues with it at all.

  6. #6
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    Re: Converting a 325 from 3.5k to 6k RPM

    Does it tap alright like that as well?

  7. #7
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    Re: Converting a 325 from 3.5k to 6k RPM

    Quote Originally Posted by pianoman8t8 View Post
    Does it tap alright like that as well?
    I tap at 500 rpm in just about everything. Biggest I have done is 1/2-28. But mostly I do 10-32 and M5 and M6. So bigger/courser than 1/2-28 I am not sure of. 1/4-20 it bangs out just fine and dandy. My only complaint is the stopping time, but that is mainly because of the aftermarket VFD I have. The original in the mill got smoked so I replaced it with a Teco. With the faster speeds it takes longer to spin down with out faulting which kind of sucks, but such is life. I would get the manual for your spindle drive/vfd to see how to modify the deceleration. You may fault yours out with the extra RPM's. They are usually pretty simple to program. It's just working through the menus and such. With the new drive I have, I can go back there and mess with all kinds of stuff really fast and it's no big deal. Having the factory parameters was also nice. I would recommend figuring out how to access them and then go through every one of them and write them down. That way if your drive ever croaks (which its probably 25 years old, minimum, so it is not out of the realm of chance) you have a copy of them and can x-fer them into the new drive. I would do this to any older machine, especially those that aren't supported well.

  8. #8
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    Quote Originally Posted by pianoman8t8 View Post
    Is your 6000rpm 325 still working well? Happy with it?
    I'm with sortafast the belt speed is high without the smaller driven pulley but I just run mine at 4500rpm to 5000rpm and it sounds good 6000rpm just sounds like it's going to fly apart! Lol mine's still running good to plenty of power still at 4500, mine still has the original spindle drive and stops just like the 3500 did

  9. #9
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    Re: Converting a 325 from 3.5k to 6k RPM

    I just bought another J325 that has the factory 6000rpm spindle and a CNC lathe if enough people wanted the factory pulley setup I could check on getting a broach for cutting the spline and start making the pulleys

  10. #10

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    Quote Originally Posted by Redzilla View Post
    I just bought another J325 that has the factory 6000rpm spindle and a CNC lathe if enough people wanted the factory pulley setup I could check on getting a broach for cutting the spline and start making the pulleys
    So far in my search I have found numerous people looking for supplier and part numbers for pulley. Is this still something you are considering making?

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