they are still expensive to build, the the pull stud clamp i just bought and it came out of China. they range from around $75 to $125. the bearings set me back $220 the shaft material was $90, the bearing lock nuts came from Mcmaster Carr and by the time they add shipping those were around $45 bearing spacers and the labyrinth seal material was from odds and ends i had so that would probably cost another $75 if you were to buy material… the taper lock pulley and GT3 timing belt came from MCmaster also and they are expensive too the die sprigs i went with i had to by 6 of them to fill a minimum order. the air cylinder i got from automation direct and those are around $150 then you get into housing material if you have to go that route? this one it’s not needed since the head of the grinder will work for that.
so they cost anywhere from $750 to $1,000 to build yourself. they sell imports that are in that same price range but who know what the quality is like? the problem with the off the shelf spindles is you get them first and build the machine around the spindle. in your case your looking to modify your existing machine so everything is custom to what you have to work with in the machine you have.
a BT30 spindle should have as close to 1200lbs of pull force as you can get. 900lbs would be the absolute lowest i would even try. i see all kinds of talk about taking the stress off the bearings with some complex floating set up like you currently have. but stop and think about how it works you have force in the spring all the time to hold the draw bar and tool holder in place the only thing you might gain is the extra force needed to unclamp and eject the holder but that only a few hundred pounds at most and it not constant. so the big thing is make sure your spindle bearings are able to handle the load
that would be my first thought for an upgrade like this. not sure what size bearings are in the PM mills. you need a 45mm ID bearing for the BT30 spindle. for this one i had to go smaller on the OD and went with 75mm od bearings so the cast iron was not getting to thin. the pulley side ended up being a 40mm ID and 68mm OD. the lager you get on the Diameter the high the load rating you gain in the single row bearings, you can always go to a double row bearing if needed but that’s pretty hefty for a BT30.
i’m not sure there is much difference between a BT30 and R8? the main difference is a BT30 with pull studs is what you want for a ATC.
it sounds like your problem might be more spring force and air cylinder related? a spindle upgrade might be the wrong place to start from a cost prospective ?
it would be about impossible for me to even get a picture of the internal work being cut. by the time you get a boring bar in the hole you can’t see a thing because things are so tight on the inside work. the set up is typical of a straight bore on a CNC lathe. i converted mine a long time ago. i just never got around to the index signal so i could thread on it. that part i had to do manually on another lathe. i would like to redo my lathe and sort that part out. i just have to many projects started. i still need to finish the table sections on the gantry mill i have been working on the past few years
The problem is that the extra few hundred pounds of force are not constant. There was a similar comment to your own at Bob Warfield’s article (scroll down to the bottom) and Bob responded by basically saying squeeze rather than push and minimize vibration and shock.
Bearings are: SKF 30207 (35x72x18.25) and 30206 (30x62x17.25), so this would require modification to the head stock. I actually plan to swap my stock bearings here shortly.
The locking dogs ensure no rotary slip and also allow for repeatable loading so concentricity errors can be compensated for. Also, doesn’t the Bt30 taper/pull stud require less clamping force to get the same holding force due to the larger taper compared to the TTS holders? Those reasoning may not be enough justification to replace all my tool holders.
I have a 2 stage 100mm bore air cylinder that allows for 42 ft/lbs of holding force in combination with the Belleville washer stack. I have the drawbar as tight as possible while still allowing for movement in the washers to release the tool when the cylinder actuators. But its not possible to use 1/2" (12mm) tools for quick roughing cuts at a DOC of 3mm.
I don’t want to hijack your build thread though with my problems! I was just curious what the cost would be for that BT30 spindle. Still very impressed!
i’m curious as to what kind of tool is causing the problems? i don’t mind getting off topic here. Tormach does some ok stuff but the TTS holders are not a all in one solution to fit every need. collets have limits but i have not had pullout issues with the R8 tapers on the Bridgeport taking 1/4 inch cut with 100% step over in aluminum. typically max depth of cut is determined by the diameter of the cutter so slotting with 100% stepover your looking at half the cutter diameter as a max depth of cut for a general guideline.
if you have any kind of facing cutter those are in a special holder that is keyed to the tool holder they make them for R8 tapers.
taper roller bearings can handle axial loads very well you have no need for concern on over loading those bearings, the dynamic loads can handle 14,000 pounds. but that type has speed limitations but those are still rated for 8000 rpm.
at that price point i doubt they meet the precision requirements of a spindle bearing. P4 or ABEC 7 is a minimum on precision for spindles.
that’s not really that big of a cut for aluminum but material makes a difference. so it depends on what your cutting. here is a link for the gantry machine i have been working on. 5/16 end mill 2.5 mm depth of cut at 20 IMP full width of cutter. ER collet holder never seen pull out on this either.
I’m curious to know the diameter of the washers in your stack. ID, OD and thickness to be more exact. i was looking into your problem with tool pull out and since your stack is in series your holding force is based on the rating of the washer working load. a stack in series just increases your compression travel and the force is based off it’s size and thickness for that particular washer being used. in series the stack has no more holding force than 1 washer of that size even though you have 8 of them in that stack. your just increasing the compression travel.
if you have a two stage air cylinder it’s not the lack force from the air cylinder. a single stage 100mm bore air cylinder should get around 1,200 lbs the one i have falls in that range and can operate well above 120psi to get even more.
i really want to help you figure out what is the problem here i don’t trust the calculations on this kit you have. if you want more force your not going to be able to get it just by compressing the washers more is a series stack.
drive dogs are in and the labyrinth seal is finished. at least now i have an idea of what the finished spindle configuration will look like from the front at least.
i did not think of it until today but i will have to make a spring tension cap on the drive end of the shaft. so one more thing to add to my to do list.
i did manage to go back and do some more work on the spring retention on the drive side of my shaft. the bolts on the taper lock pulley were in the way so i had to add a little bit of clearance to clear those but that part is sorted out. i did notice my ejection stroke was longer than what i expected so i will have to go back and rework that part of the internal work of the shaft. keeping the ejection as short as possible lets you keep as much of the pull force on the drawbar to hit your target force and not waste it on the ejection stoke.
one other thing i will ad to this is an end cap to the threaded drawbar to protect the threads.
i did start working on the bores in the casting but that is going to take some time. i decided to order a cylinder hone to finish the size on that part the cast iron might be heat treated? seems a bit tough for cast iron. this machine was built in a time when they tended to do things right so the quality is better on old stuff just about all the time. now days it’s about profits and doing stuff cheap.
the housing part of this conversion is a bit tricky on a manual machine the bores are straight forward but the shoulders at the end of the bores have to be flat and square so once the size is done on the bore i will have to set it up on a rotary table to kiss the flats off being careful to not hit the finished bores. bearings have a radius on the corners so if there is a little bit of extra material in the corners it does not matter. the important part is the depth being equal all the way around. the final depth can be accounted for in the bearing spacers for final fitment of the shaft to the housing.
i have been waiting for 3 weeks for some DOM tube so i can make outer race spacers and this material still has not shipped yet? prices are a bit out of control on tube and everything else for that matter but it is what it is i guess.
i do have enough finished that i can sort the motor mounting and everything else. this is still in the rough design phase and i still have a few things to sort out but the major stuff i think i have sorted out and did a screen grab to post for the basic plan.
since i would like to do rigid tapping this 3 phase motor needs some feed back so coming up with a way to get an encoder on the motor was a bit of a thinking process but i think i have a good plan, the motor has a plastic fan for cooling on the back side of the shaft so the plan is to attach an encoder directly to the shaft and loose the plastic fan altogether. these motors cool ok at high speeds but when you run slower the cooling drops off. so to make it better at all speeds the plan is to heatsink the motor and use 2 DC fans to cool everything. most likely they will just run all the time when the machine is running.
i have a simple belt tension system worked out and now know what length of belt i need. the one belt i have is too short but getting one that will work is not a problem.
this is still a work in progress but the screen grab explains things better than i can i think
good news is my DOM tube i ordered on 12/192021 finally is moving along in the shipping process i also sawed up some material and have all my blanks for the model i just made up.
i also ordered a rotary encoder for the motor. but went with the hollow shaft design to make life simple. amazon has some sketchy listings and the information is not so great so hopefully it’s what i think it is and not something completely different? when it comes to encoders it gets confusing with the different options. it would have been nice to fine one with 5/8 bore but they were way out of my budget so i will have to alter my motor shaft to fit the one i got.
with the hollow shaft style encoder it very well my fit under the cover for the stock fan on this motor once i take the fan off? if not the cover is just plastic and i can make it fit one way or another
just some progress pictures on the motor upgrades for cooling. i still have to get back to the spindle spacers but it took a month to get the DOM tubing i ordered so i was well into this part by the time i got my material.
i have to open up the plastic cover on the back of the motor so when i add the encoder it has a neat and tidy look to it. this was just a quick assembly to check fit and function so i took some quick pictures to share.
just some more pictures of it all wrapped up and the encoder mount. i had to cheat a little and make a long allen wrench to get to the set screws on the encoder. a standard length wrench was to short. the hole in the bore of the encoder mount is in line with the set screws and you can see a hole in the plastic cover that lines up so you can put everything together.
the casted end cap of this motor had a slight contour so i had to spot a face so the encoder mount would sit flat. the undercut on the mount is just clearance since the center of the casting was not machined. these castings are paper thin to begin with so min. clean up on just the area where the outer face of the encoder mount sits is all i wanted here. finding a way to hold onto the casting and miss all the ribs cast into the under side was a treat as well
just some more pictures to share with anybody watching this the old grinder had a direct drive so the motor was on the end of the spindle. since that has all changed and this thing is no longer a grinder the motor got moved to above the spindle shaft so i could do the drive belt and and keep the shaft end open for the air cylinder eventually for the power draw bar for the BT30 spindle. the old drive for the head was a gear drive running at a 4:1 ratio, since the ball screw is only a 5 mm pitch that would make for a really slow axis. i was able to switch to a 2:1 ratio on the gear drive and keep the same center spacing on the gears. after looking into operating speeds for this gear drive i can run up to 4500 rpm on the pinion gear and and the ball screw will run at 2250rpm which with the speeds on the servo will put me around 450IPM on the Y axis which is my heavy lifting axis, mechanically the X and Z axis could run as high as 1000IPM but that will be adjusted down based on how much screw whip i would get? the screws are shot and if they where supported on the ends this would be no issue but since they float on the ends 500IMP would probably be more realistic. no way to tell until you start spinning them and see exactly what happens.
backlash on the gear drive is something i will keep an eye on since i want it to be as tight as i can keep it. running duel loop feed back will account for this but you still want to keep things as tight as possible mechanically.
one issue i see already is back driving on this axis. lifting and holding it is not an issue but the back driving is not good so i have a plan for that part. if power is lost in the middle of something bad things could happen.
my plan is to make a counter balance from an air cylinder and will be a closed loop low pressure system. Haas Automation did something like this with an air over oil type system so this is a spin off from that concept. i don’t expect it will hold air for ever but a cheap solution to a constant force counter balance.
my spin on the air cylinder as a counter balance. works the same way the Haas system works just not as heavy duty. the Haas machines are dealing with a lot of weight so they did an air over oil system.
after paying around with it i landed around 200lbs for force in the upward direction to even out the force needed to lift and lower the head. i don’t have an exact weight of the head but everything is in the ballpark of 275 to 300lbs.
i was going to have a regulator oiler combo on the counter balance but decided it probably would not do much since the air is not moving around very much and just used a regulator water trap on that part and put the oiler on the section that controls the air pressure for the power drawbar. you need two regulators since the system operates at 2 different pressures.
basically you turn a air cylinder into a adjustable constant force air spring doing this. the upper zone just either push out air on that side or pulls air in depending on the direction your moving. pretty basic system. the portable air tank is just a collection point to store the air pressure and you tank has to be 10 to 15 time the volume of the air in the air cylinder.
I have been working on a chip cover solution and came up with this. they are a bit crude but they will do what i want them to do and keep most of the chips out of area’s they should not be
i picked up some more linear scales and 2 of the three are easy to mount the Y axis i will think about for a bit.
i still have a ton of things to sort out but it’s slowly moving forward.
just passing the torch to you young folks when i first started messing around with this stuff the information was really limited back then. now days information is all over the place and parts can be had for cheap if you need them to be or at least for now anyways. the mechanical is no doubt my stronger point so when the electrical stuff comes into play it going to get crazy with this being my first time at Linux CNC.
Linux CNC seems to be about the cheapest solution to more complex control like a fully closed duel loop system. so hopefully i can fumble my way through all the set up since it is way more involved with a Linux.
once i get my feet wet and get more comfortable with it it should open up the doors to a lot of things so if i can get my act together and get things finished up i can move on to other stuff lack of free time is my biggest problem
Part of the trouble with the oil point connections was the need for some of it to be able to move with the saddle and table on a few of the connections. all the bearing blocks and ball nuts have a M6 x 1.0 hole for the grease fittings they come with. i had a bunch of 10-32 barbed fittings ( will probably need another pack of 10 ) so what i did was get some brass M6 x 1.0 bolts and tap the head so i could attach the barbed fittings and put around a 3mm through hole in the bolt so the oil can flow through it.
i also gutted the old control box and stripped it down bare and put a fresh coat of paint on it to freshen it up some. I got that back on the machine in the original location and ran my VFD cable into this box. the plan is to use this box for the VFD and probably some DC power supplies to keep it away from the sensitive stuff. the braking resistor i will probably mount out side somewhere since they generate some heat. i’m not sure if it would be wise to mount it in the box?
i have check vales for all my oil points too. i just have to sort that end out still. i was try to use the old manifolds for the oil lines needs but i might have to make something custom since i have more points than what was original.
not much progress but the way oil pump in mounted and the lines for the head axis was already done so i reused that part and it’s hooked up. the rest i will most likely end up making taking a guess. but here is a few pictures. everyone like pictures
the die sprigs i went with i had to by 6 of them to fill a minimum order. the air cylinder i got from automation direct and those are around $150 then you get into housing material if you have to go that route? this one it’s not needed since the head of the grinder will work for that.
i don’t trust the calculations on this kit you have. if you want more force your not going to be able to get it just by compressing the washers more is a series stack.
