Planetary speed increaser

[Coopertje]

Did I ever mention that I am much better in starting projects then on finishing them  While I am scratching my head on the Boxford tooling I had some time left for a nice in-between project. At this moment I try to focus on my machines and tools and try to get them completely finished including the desired accessories. I am sure the invested time will pay off when getting back to the model engine building..... Recently a friend of me mounted a Kress high speed milling tool (max rpm is 25000!) on his PCMill. I did not believe this would be good for home shop machining, expected to smoke up the tooling etc. When I got a demonstration I was totally surprised on how well it worked out. Normally I use 2000rpm for a 6mm end mill in aluminium with a feedrate of 150 to 200mm/min max, but the machine makes a little noise and vibration. The finish is good but it does not sound optimal. When running with the same operation with 20.000 rpm and a feedrate of 800 to 1000mm/min the machine was absolutely quiet. It went trough the job 5 times quicker and the machine did not make any noise nor any vibration. It sounded like a very happy and satisfied machine. The mill used was not a new one, standard second hand purchased HSS mill. Then I was convinced that this is the way to go for me too. I am planning to start to do more on 3D and 4D milling so higher feedrate are more then welcome!   

I want to keep the original head on the PCMill for now as I have a nice collection of SK-30 toolholders for it. Removing the original spindle, mount a bracket with a Kress and swap it again for the original spindle is something I will not do, I know myself. So I need something that can be easily attached to the original spindle.  First thought was to mount a Kress milling spindle on the side of the milling head. It will work if I mount the work offset on the table (PCMill has an X-axis travel of only 200mm), might need to build a table extension for clamping, but I would be able to use the complete X-axis range. The second option is to build a speed increaser using planetary gears. Did some reading on this and found that cordless drills are a nice source for planetary gears. Cool, I happen to have 3 available with broken batteries. So I decided to build a speed increaser myself, if it turns out it will not work in the end I can always mount a Kress on the side of the machine.

Took out the gearbox of a Bleck&Decker drill and it had a double planetary gear box. Total reduction was a factor 32. It had one set of plastic gears and one set of steel gears. When using just the pair of steel gears it will give me a factor 5.2, max rpm of the spindle is 4000 resulting in a speed of 5.2x4000= 20.800 RPM. That will do for me! Did not make a design, will see how the device develops as I go.

I will use the original shaft as input shaft together with the cast steel bearing bush from the cordless drill. Would be better to use ball races but I do not have them. Try to build this one with materials available. Reduced the height of the cast steel bearing bush and cut a new groove in the shaft to take the “spring clamp” (sorry do not know the correct name for it) keeping the shaft in position. Cut  a piece of alu tube (50x28mm) that will take the ring gear.



Cleaned up the outer surface of the alu tube and with a boring bar turned the inner side to the correct diameter. The ring gear is a light press fit. On the bottom side you see that I kept the diameter smaller. By this I am able to clamp the ring gear with the cover that will hold the input shaft.







Next was the upper cover, will be made out of aluminium too. To have it as centric as possible I cut the complete outer shape as well as the internal boring operations in one single set-up







Mounted the cast iron bush, got a nice fit! The black ring in the bottom of the next picture will prevent the “spring clamp” to open by itself under load.







I have a gap of approximately 0,1mm between the end of the ring gear and the satellite gears



Next will be bottom cover that will hold the spindle.

Regards Jeroen

[kvom]

Nice project!  I could use one of those myself.  It will be interesting to see how much runout the finished device will have.

[Coopertje]

Thank you Kvom. To be honest I am not concerned about runout, if you work accurate you should be able to reach 0.01mm or better. I am more concerned about rigity during milling because the spindle is quite short. I plan to mount the complete tool in a bracked that will be bolted to the original milling head. Lets see what will come out, no money lost when it turns out not working. At least for me its a lot of fun to make this little tool. Hope to post some more progress soon.

Regards Jeroen

[Roger B]

An interesting concept  I hadn't thought about the large number of dead battery drills out there as a source of what look like quite high quality epicyclic gear sets. I have other uses in mind but will be interested in how your milling attachment works 

[Coopertje]

Hello Roger,

They are a nice source indeed, there is nothing wrong with these gears. They should be of good quality considering the forces they will face in a cordless drill. I am glad that I did not throw them away, especially because the new generation have much better lithium batteries that do not self-discharge so the machines will last for much more years then the old ones.  The broken battery ones might become rear in future 

Regards Jeroen

[PStechPaul]

Beautiful workmanship on that! I hope it works well for you. I would be a little concerned about 20,000 RPM unless the gears and bearings are made for such speed. I have mostly worked at very low speeds and I also have noticed a lot of noise - maybe taking it up a notch or two might improve things, like a Ferrari instead of a tractor! 

[Coopertje]

Thank you Paul. The gears look and feel that will be able to handle it, time will tell! The bearings I have are the SKF6000Z, they are specified up to 34.000 rpm so I should be more then ok with my 20.000. About speeds and feeds the same here. I tend to use too low speeds and feeds to protect my valuable mills. Somewhere between the Tractor and the Ferrari is the optimum. I have no any education in machining nor mechanics, learned all I know by doing. Guess the same applies to find the correct speeds and feeds that work on my equipment. When my machines sound happy I am happy!

Regards Jeroen

[kvom]

I use G-Wizard program for speeds and feeds, at least for a starting point.  Generally there is no max speed for aluminum, so I run my mill at max RPM (only 4K) and feed is set for chip load and SFM.  I did a run for a typical slot in aluminum on my mill at 4k RPM and got as feedrate of 21 IPM.  If I could run at 20K, my feedrate would max the mill at 75 IPM, but the recommended rate is 106.

But as you say, the sound will tell you if the mill is happy.

[Coopertje]

Thanks for the tip Kvom. Should start to use such a program to get at least a direction. The speeds and feeds you mention for aluminium are quite simular to what I use, 200mm/min at 1500 rpm. I prefer to stay on the safe side.

Regards Jeroen

[crankshafter]

Hi Jeroen.
This is a nice pice of work.
I have one thing to mention, i think you have used wrong circlips to secure the shaft/bearing, it seems you have used (pic. 9-10) internal clips instead of externals on the shaft? but i like your solution, mather of fact i have had something like
this going around in my 
Some years ago i converted a toy Ferguson pedal tractor to electric prop. for one of my grandsons. Using a drill planetary gear. Scored some points on that one

best reg.
CS

[PStechPaul]

I think you are right about the retainer clip. I thought it might be an E-clip, but it looks more like an internal clip

[Coopertje]

Thanks for pointing that out CS, seem to have forgotten the purpose of circlips and eclips. You are correct Paul, it is a circlip. I will forward your comment to Black&Decker  This is the way it came out of the cordless drill, just cutted the groove on a different position. Its ok though, the inner diameter of the black ring is dimensioned such that it presses the circlip inwards. Guess this will give the same effect as using the eclip.

If the device proves to work ok I will remake this part anyway and replace the cast iron bearing bush with a pair of ball races. With this I will not have space anymore for the black ring so I should use an Eclip instead... Almost finished the spindle holder, will post the pictures as soon as I have finished it.

Regards Jeroen

[Coopertje]

The bad news is that there is just a little progress and the good news is that there is a little progress. Finished the spindle holder. The actual spindle will run in 2 SKF6000ZZ bearings, as mentioned before they are rated up to 34.000 rpm. Checked up a piece of 50mm aluminium and shaped the outside. The spindle noise has a diameter of 30mm. The inner side is drilled 23.5mm and used a boring bar to cut the seat for the ball bearing.



Mounted the 4 jaw and flipped the part. Clocked it to run within 0.01mm centric and cut the seat for the second bearing.



And cut the centring flange. This will centre the spindle holder when mounted to ring gear case.



Drilled the 6 mounting holes 3.2mm by using the hole function on my DRO. Works very well, much quicker then to set-up the rotary table and crank it to the correct positions. Made a counter sink with a 5mm end mill.



Mounted the pieces together and took it to the lathe to clean up the outside of the complete assembly to have exactly the same diameter on all 3 pieces.



Used a machine vise to press the bearings into the housing. This ensures that to go in straight.



Below the result with bearings pressed in





Up to the spindle now. I have a spare set of 8mm collets that I bought on some show for a few Euros. They are perfect for this project!

Regards Jeroen

[PStechPaul]

That's some very nice work! 
 
Not having seen your milling machine, I am not sure just how this all fits together. To do the same thing on mine, I would have to have a MT2 taper on the input shaft, to mount in the spindle. Then the housing would have to be immobilized by clamping it to the quill, or ram, which can move up and down but cannot spin. Then the output shaft would need some sort of toolholder, probably a collet, for the tools you want to run at the higher speed. I would assume that these would be smaller end mills with perhaps 1/8" (3 mm) to 3/8" (9 or 10 mm) shanks. Also, I would assume that the output shaft would have some sort of high speed thrust bearing if you wanted to do any plunge milling. I am sure that you "got this" but I am just interested to see the concept of the end project. 

[Coopertje]

Hello Paul,

Thanks for your comment. You are getting the picture bright and clear! This is exactly the plan of attack. My CNC mill is a Emco PCMill 55, it can be seen at “http://www.modelenginemaker.com/index.php?topic=3521.0”.

The outside of my device will be clamped in a 15 to 22mm thick aluminum bracket that will be bolted to spindle housing, so it will move up and down with the original milling head. The bracket will give maximum stability and it will take away the load on the input shaft that has a simple cast metal bearing bush. The input shaft will be hex-shaped and driven by a SK-30 adapter with a hex hole in it. The speed increaser can slide up and down in the SK-30 holder eliminating accurate mounting needs. The collet set I have available for this project has a range between 1mm up to 6mm max, which is sufficient for my size of machine and projects I plan to do on it. 
A angular contact bearing would be ideal. I will just use 2 simple ball bearing in this device, the idea is to make this from materials available and verify if it will work in the end or not. When it is a proven success and the normal bearings will not survive I can invest in a good angular contact bearing. Up to then I will tell my CAM software to use Spiral plunging instead of a straight plunge into the work piece. For my feeling the load on the actual end mill reduces with the increase of the rotation speed. This assumption is based on the fact that the machine stooped to make noise and small vibrations at high RPMs. So the 2 standard bearings might be more then suitable for this….. Time will tell…..

Regards Jeroen

[Coopertje]

Did some work on the spindle / collet holder. Roughed out the basic shape from 20mm steel and did not care at all about surface finish.



For finishing I took a grinded carbite insert and turned it to 3.16mm (this is the inner diameter of the gear), 10mm for the shaft and 14mm for the thicker part. I left a small ring of 13mm that will seat against the inner ring of the bearing.



Cut the groove for the E-clip



Took it out of the lathe and showed it its new house before cut it off the bar



Back to the lathe to cut the seat for the collets. The collets have an odd angle of 17 degrees. Set the top slide to 17 degrees by eye and fine tuned the position using a indicator. Used the 4 jaw and clocked it to be within 0.005mm.





Finally a usecase for my small boring bar that I have purchased one year ago on a show, sorry for the blurry picture



Cutting went fine, made several small steps and used the collet as a depth gauge.



Time to cut the tread so that I can mount a collet nut. The tread is M14x1. Start is quite close to the live center, went ok though without any collisions



Below a family shot of the parts made so far



And the spindle mounted in its new home.



As you can see I also cut a flat part to be able to mount the small gear. During cutting this flat I noticed that the shaft was a little loose in the 3-jaw chuck, did not want to damage the M14x1 tread.. So I tighten it a little more and forgot to retract the mill  result is that in what should supposed to be the finish pass I took off too much material. Will fill it up with some JB weld and see how it holds....

Thanks for watching, regards Jeroen

[dieselpilot]

How much preload do you have on those bearings?

Greg

[pgp001]

Hi Jeroen

Could you give me some information about that rotating tailstock centre with the slim nose please.
Is it a commercially available one or a home brew.

Thanks
Phil

[Coopertje]

Greg, to be honest I don’t have a clue about the amount of preload. All I know is that the E-clip needs to be asked very friendly to go into position with the help of a screwdriver. There is no axial play at all while the spindle rotates freely, for me that does it…. Do not know if this answers your question, if not let me know.

Phil, it is a commercially bought set from Vertex, google on “Vertex vlc-313”. The set contains several inserts, very handy and nice quality!

Regards Jeroen

[Coopertje]

The collet nut is made out of 20mm steel bar. Cut off a piece, drilled and tread the inside with M14x1 to meet the spindle nose. Made the tread completely trough.



Cutted a recess that will hold a ring which presses the collet in its seat.



The ring is a simple turning and drilling job. I drilled the hole 0.5mm bigger then the outside of the collet. Fluxed the parts and silver soldered them together



Took it back to the lathe and shaped the front side



And of course a test fit on the spindle





When milling the flats on the collet nut I guess my mill became hungry, it tried to eat it     Stupid me, did not tight the C5 collet enough...



Finished milling the flat sides and took it back to the lathe to clean up the mess caused.



To protect it from rust and to give it a nice look I dropped it in the blackening bath and hang them to dry.



That’s it for now, weather is too good over here to spend too much time in the shop!

Regards Jeroen

[gerritv]

I would have called that whoopsie a new style of knurling
:-)
Gerrit

[Coopertje]

  That sounds much more positive then calling it a mishap Gerrit! Lets call it "the free style knurling method"

Jeroen

[dieselpilot]

How did this work out?

[Coopertje]

Hello Dieselpilot. Do not know yet,shop projects are on hold at the moment. SWMBO orderred me to finally finish the rebuild of the attic that I started over a year ago. As normal the last 20% takes 80% of your time, but the end of the tunnel is insight. Hope to pick this project up in a couple of weeks.

Regards Jeroen

[Coopertje]

Finally daily live got out of the way and I was able to catch up this project. I did not like the cast iron bearing from the original drilling machine so I decided to make a new one with ball bearings inside. Think the photos speak by themselves, if there are any questions or remarks feel free to ask them.
 
















Next part will be the mounting plate that will be mounted against the milling head and holds the speed increaser.

CU soon again, eager to finish this one and test it!

Regards Jeroen

[Coopertje]

Made some more progress this weekend, made the adapter plate and fixed it to the original milling head.

First step was to face mill a piece of 20mm thick aluminum plate





Took it to the lathe to turn the socket in which the speed increaser will be located. Since the exact center hole position is not so critical I took the easy way and used the live center to set up the 4 jaw chuck. The mounting holes will be derived from this center hole afterwards.





Then swapped the plate in the 4 jaw and now I spend a little time to set-up to the exact middle position. This side will get a ball bearing to support the SK-30 holder that will drive the speed increaser. The input shaft of the speed increaser will get a hexagonal shaped axis. By this construction I do not need to worry about the exact hight between adapter plate and SK-30 holder, it can slide over the hexagonal shaft, hope its clear what I mean.





Back to the mill and drill the 6 holes to put the screws to secure the speed increaser body to the adapter plate.



I am happy, the speed increaser body is a tight snug fit into the adapter





Disassembled the milling head from the PCMill and put some painters tape to protect the paint work and to scribe the lines for visual check before drilling. I use the DRO for exact locations. I must admit that I really hate to drill holes in my machines, if there is any way to prevent it I will follow that way for sure. In this case however I could not see any other option to make use of existing holes. Also they are located on the bottom of the head, normally invisible for the eye. The holes are treaded M6.





Last picture is a family shot of the adapter and milling head.



Last item to make before I can test if this thing will work or not is the SK-30 adapter. It will get a internal hexagonal hole….

Regards Jeroen

[Roger B]

Almost there    I will be interested to see it running. I have a small Proxxon drill modified for milling that will give me 8000 rpm.

[Coopertje]

Hello Roger, thats probably the best solution. You can get for example a Kress mill for not too much money and that will give you 25.000 rpm. Simple mounting bracket and off you go! The only thing that made me try this way is the fact that I am not looking forward to remove the milling head every time I want the high speed. Mounting it beside the original milling head is another option, but due to the small travel of the X-axis (200mm) I will loose too much wring area. If this speed increaser will not work as planned I think I will mount a Kress beside the milling head an make a extension on the milling table so the complete travel will be offset. For now I hope this option is not necessary.

Regards Jeroen

[Coopertje]

Finished the SK-30 adapter to drive the speed increaser.

Started with broaching a 8mm hexagonal hole in one side of the blank



On the other side of the blank I tapped M10 and made a pocket to center the pulls stud ( :hammer bash: messed up the bore, had to loctide a bush and redo the pocket)





Then I chucked up an original SK-30 holder to set the cross slide to the correct angle



And turned the taper step by step







I checked the final dimensions using a profile projector I purchases some months ago. It a nice device to accurate measure odd shapes.





The end with the hexagonal hole will run in a ball bearing seated in the adapter plate. This makes it easy to line up the adapter plate when mounting it on the milling head.







The input shaft should of course also get a hexagonal shape, clamped it in a C5 collet and used the hexadapter to mil the 6 flats





Below some pictures of the completed speed increaser







Family matters are waiting for me now, beginning this week I will mount the milling head back to the mill and start to do some tests. I will keep you posted on the results, hope I can post some positive results!

Regards Jeroen

[Coopertje]

It working  Not upto the 20000 rpm, its ok upto 12000 rpm. Above this speed it starts to make noises indicating the gears are not happy anymore. The runout in the collet holder was a little disappointing, a little less then 0.02mm, I aimed for better. At least its good enough for the purpose I have in mind, full 3D milling with a small radius mill. I have made a video of the speed increaser milling in aluminum with a 6mm 2 flute end mill.

<a href="https://www.youtube.com/watch?v=T1TEbbZe7nw" target="_blank">http://www.youtube.com/watch?v=T1TEbbZe7nw</a>

If the device proves to be stable over a longer period I will mosr likely invest in a angular contact bearing to eliminate the radial and axial play (although at this moment it is neglectable).

Thanks for your interest and let me know if there are any questions or doubts.

Regards Jeroen

[Tjark]

Jeroen, I have watched your work on the side line and wondered how easy you went from idea to a practical useful tool.
Very nice work, hoping you can use this tool for a long time without troubles.

  Tjark.

[dieselpilot]

Very good. If you're happy with the surface finish it offers, you've succeeded. I think you would see a significant improvement with good bearings and reduced spindle runout. I suggest mounting a very sharp carbide tipped boring bar in the vise and writing a program to true the collet taper in the beraings. I did this when the second shaft in my spindle had too much runout. I had to replace the shaft due to a crash that bent my original spindle shaft. The runout and fit of collets has been excellent. That planetary gear looks a little light, though time will tell.

What is the resolution of your PC Mill 50 after conversion?

Greg

[Coopertje]

Thank you Tjark, once you have the right idea in the head its just a matter of making swarf. Makes a difference that it is not a very complicated device to make.

Greg, I am quite happy with the finish, looks good with a additional finish pass between 0.1 and 0.2mm.  I expect that this will the MKI model and will build a MKII version with improvements on spindle bearings, most likely some quality ER-11 collets (the collets used  in this one I picked up one day on a show and they are not in a perfect state). I am quite sure that the bearing is responsible for the run out, I was very careful when setting the spindle in the independent 4-jaw. I have thought the same as you suggested, mount a small milling spindle (or what you suggest a small boring bar) in the vise and grind / turn the collect holder true when mounted in the machine.

The PC Mill 55 has a standard step resolution of 0.005mm. Since I use the original drives (designed an interface board to translated between the differential Emco drives and the standard TTL logic on a break-out board) this resolution is not changed. The spindle pitch is 10mm and in Mach I have 2000 pulses per rev. -> 10mm/2000p= 0.005mm/p

Regards Jeroen

[Roger B]

Looks good to me  and does what you expected    Excellent job 

The collets you have look to me like DIN 6343 dead length collets rather than ER 11. The ER (extended range) collets are tapered and split from both ends.

[Coopertje]

Thank you Roger. You are very right, the collets used are not ER-11. What I meant was if I make anotherone, the MKII version,  I will use ER-11 collets from a good quality to improve total runout of the spindel.

Regards Jeroen