High speed CNC spindle

[mu38&Bg#]

It's OK. My current spindle is a problem so I'll know the weaknesses when the new one gets going. The bottom plate likely needs reinforcement.

I didn't have a cutter to slot the mount with so it will be tomorrow evening.

 

[mu38&Bg#]

The spindle mount is done. The spindle is balanced. I ended up removing a lot of weight I added. I did something wrong along the way. Now, I just need to put it all together. I'll have photos and video later. EMC2 is talking to the RC speed control, but scaling is incorrect, it will work for now.

Greg

 

[mu38&Bg#]

This is a picture of the mounted spindle. I did rebalance before putting it in the mount. I ended up removing some weight I added. I figured out what I did wrong, but didn't redo the nose end of the spindle so I think this is the problem. I also have doubts about the supposedly balanced collet nut I bought. I did run the spindle mounted to the mill, but there was some vibration I wanted to check out. So it's off again. Then I spent a couple days cleaning the shop getting ready to move everything to make room for the next project, the Emco lathe retrofit. Hopefully I'll get this balance issue sorted tonight and I can make some chips on video. tomorrow.

Initially, the no load currents were very high, like 20A at 22V input. They quickly dropped to under 4A at 22V. This is about 15kRPM. I checked the old spindle I was using and that was about as fast as I ever ran it, so the 30k idea might be way over the top. There is 90W of heat without load at 22V. The bearing housing and mount appear to stay fairly cool, the motor gets hot after a few minutes. I think I'll have to order some material to make a water cooling sleeve. I think the bearings are also over the top for the cutter sizes anticipated. I see some things I would have desinged differently, namely providing better access to the nose end of the spindle for balancing.

Greg

 

[steamer]

Is most of the 90 watts at the motor?....You may be able to sink that and use a fan...

Looks Great!



Dave

 

[mu38&Bg#]

WooHoo!! I finished the rebalance and checked the collet nut. The collet nut I bought that was to be balanced wasn't! Oh well it's still a nice bearing nut I'll use with the Arboga. Instead I balanced the original nut that came with the collet holder and it turned out reasonable.

This is the first part!



And, some video as promised.

[ame]http://www.youtube.com/watch?v=fGrITuuTZtQ[/ame]

Dave, yes most of the heat is the motor. I ran this part without cooling and it ran for 30 minutes. It was OK. I don't know if the change in temperature of the aluminum mount and block is worth worrying about. I thought about running the coolant through the mount. I'd rather use a fan if I could.

Greg

 

[steamer]

Hey Greg!

Awesome! Looks and sounds great! Congratulations...now you know why those spindles cost so much! ;D

You did a great job!

As far as the heat, always take the heat out where it's generated first ...if possilble
I would first try a heatsink and fan on the motor casing, keeping the temperature distribution as symetric as possible....ie even all around and along the length.....this is technically impossible, but strive for it. A coaxially mounted computer fan blowing along the length of the motor will give a symetric air flow around the motor and should be simple to do. You will need some air flow though!

If you can dump 90 watts with a heat sink and a fan over a relatively small temperature differenc, you will have a very simple system without all the grief of a fluid system...trust me on this you will be better off if this works out.

If it doesn't work out, and you go with a liquid coolant...the same rules apply. Flow rate is your friend, as it allows you to remove heat across a smaller temperture difference.

Congratulations Greg! Ya done good!,,,nice machine....I would like to know more about your composite base. I'm used to granite and epoxy/granite, fee free to start a thread on that if you like.

:bow:

Dave

 

[mu38&Bg#]

Dave, Thank you. I'm very happy with it. If I bought the bearings at retail it would have been 400-500USD, in bearings alone. I already had the motor or that would have been another 290USD, although I could probably use something smaller. I am going to try a heat sink and fan.

The base of my mill is a piece of quart countertop material. I'd have to check, but it's about 1.25" thick. Initially the idea was to use a 18x24x3" granite surface plate I purchased cheap. But to fit what I thought would be enough column it came up just a bit short. I think this is the weak point in my machine right now. I've been thinking for a long time to epoxy some steel angle or channel to the bottom to improved rigidity. This machine was built in 2004, before I even had my first lathe. The idea came from reading Swede's 5bears.com site when he built his. I didn't have access to any metalworking equipment and I was being cheap, so that was what I came up with. The linear slides are Aerotech Accudex units. 12" X and Y and 6" Z, and they do very well. The resolution of the axes is 2 micron by the encoder, and if i remember from the specs this is also the repeatability for the ones I have. The Z axis is too light really, and I might build one if I can't find something I like on Ebay. I do have a large 24" slide of some kind I bought for a different project a long time ago, and I'd love to make X travel 24", but that entails a lot of down time unless a build a whole new machine frame and transfer parts. Anyhow, the next step is to finish a 4th axis I started just before the spindle and build some projects that have been waiting for that.

Greg

 

[petertha]

Your spindle construction is such a cool project. I know virtually zip about CNC or spindles or their running environment, but I DO recognize the round black thing in the end & practically consider myself an expert in the many ways to cook them! (F5D racing) ;D

Somebody smarter than me could do a heat calculation, but my gut sense is if you are running 30 minutes with moderate temp buildup now, you could probably cool it with some combination of heat sink type fins + DCV cooling fan(s) lik in PC's. I’ve seen RC heli & car world installations like attached pics, where their motors are also confined to dead air. Maybe a scale-up & better orientation?

In/out water jackets like these are quite common for RC boaters.
http://www.offshoreelectrics.com/products.php?cat=Motor+Water+Cooling

The jacket & basic plumbing would be easy with your machining skills, but replacing the ‘lake’ with pump & exchanger hardware like PC liquid coolers looks a bit more complicated. Im not sure what heat wattage values they handle, but they have the ingredients to modulate it closely if thats an issue.
http://www.koolance.com/technical/howtobuild/index_01.html

 

[mu38&Bg#]

Hey Peter! I've been playing with electric airplanes since 1997 or so. Flew F5D 1999-2001 or so. I went to the F5 worlds in San Diego as a mechanic for the F5D team. I used to work for MPI who sells Himax motors. Been bust with other stuff. I still need to look at the figures. I saw only 8-9A while cutting under load so the motor is still only 50% efficient at best. Regardless the heat load is fairly low. It's possible that I'll make a new motor housing incorporating the cooling fins. Right now I'm doubting I'll run 30kRPM, so I might change the stator out for a lower KV and run higher voltage. For water one of the 56mm jackets would work. Thanks for the link. That would be the easy solution now as I have a chiller on hand.

 

[steamer]

That Traxxas block looks familiar greg!....except mine was 16" in diameter! :big:

Can't beat the price!

Dave

 

[mu38&Bg#]

I ordered a 56mm water jacket. I'll see how that does when it comes in. I've made a few parts and it looks like the crossed roller bearings in my Z axis needs to be tightened. The spindle looks good.

 

[mu38&Bg#]

The water jacket arrived. I installed it and connected it to the chiller I have. I didn't make the jacket because I thought for such a simple part, how bad can it be to buy some Chinese import? I had to reinstall one hose fitting and one of the O rings barely holds water. : The chiller certainly does it's job and there is far more capacity for cooling than needed. I don't feel like making a heat sink for air cooling right now, so the machine will run like this until that time comes. I still have to find my high voltage RC motor controllers to try the 48V I intended. While I didn't think I would need it things have been running very well.

Today, trying some new feeds and speeds, I set it for 4mm deep cuts and 10% stepover at 1000mm/min with a 1/4" 3 flute at ~15kRPM in 6061 aluminum. This was running pretty well when, all of a sudden, it does a full width pass! I know that Visualmill does this to me every once in a while but didn't check this part. I was reaching for the Estop when it plowed right through without slowing. I'm still running the spindle on my bench supply and watched as the current jumped to 23A(~500W) on the other side of the part in another full depth pass. I have to say I was mighty surprised when things didn't go awry. The rigidity of the spindle and large bearings really pays off. My mill seems to be doing well also, just the Z axis may need to be tightened or replaced with something a bit more sturdy.

One thing for sure is you want good collets at these speeds and feeds. I did some parts with a .070" endmill which I used a nice Lyndex ER16 collet for and that really ran well.

Greg

 

[HS93]

Have you seen these they will take 50v , I have had a few for boats for a few years and they are one of the only speed controllers that have a repair service, and for you American made


http://www.castlecreations.com/products/phoenix-ice2-hv.html

Peter

 

[steamer]

Congrats Greg! Well Done!

Glad she's more capable than you originally suspected!


Dave

 

[mu38&Bg#]

Yes, I'm a fan of Castle creations. I bought controllers from Patrick when he was making them in his basement and sold them when I was in the business. I do have a PH-45HV ....somewhere. I'm checking Ebay for a suitable industrial control that will integrate with the control a bit better.

Greg

 

[petertha]

...4mm deep cuts and 10% stepover at 1000mm/min with a 1/4" 3 flute at ~15kRPM in 6061 aluminum. .. all of a sudden, it does a full width pass! Greg

Youch! One thing your awesome build thread made me realize is how little I know about spindles. I have come to appreciate they are not just a shaft running in some bearings!

When you sized your spindle bearings & internals, how do you determine the max side load it sees in typical/max depth cuts to begin with? Not sure if 'side load' is proper terminolgy, but I mean the force that the shaft/bearing see in the x-y plane of a cutter vs the downward plunge force in the z-axis?

Reason: my understanding of spindles in specialized grinders (toolpost or tool cutter style) similarly require tight tolerances at high rpm, and obviously some force. How does one get a handle on this infomation? I also noticed a few spindle variations on Quorn-type tools where the motor is remotely driving. I ordered this book for some basics.

http://www.amazon.com/dp/1854861492/?tag=skimlinks_replacement-20

 

[mu38&Bg#]

I still don't know that much about spindles. I did learn that I could make a better one now. There is a lot of information in the machine bearing catalog in the Timkem lineup. Check all of the manufacturers machine tool bearing catalogs for references. Cutting tool power can also be calculated. This one from Mapal is good.

As long as the motor can keep up, things will be fine. My DC bench supply is a 2.5kW 46A unit. Had I set the current limit less than 25A or used a lesser power supply the results would have been very different.

I did break a 1/4" end mill yesterday. I tried finishing the part with 4mm deep passes, but it got too hot and clogged the cutter. The endmill has a lot of use, so it was probably dull too. I learned when I had my old spindle to do shallow passes at large step over while roughing to avoid overloading the spindle if the CAM threw a random full width pass in there. After the tool broke I went back to .75mm, 75% step over and finished the part. The run time was essentially the same and I could have skipped one operation that I felt was needed when I was using the deeper passes. So, it would have been about 10% faster. I might look at G-Wizard to assist with feeds and speeds.

Greg

 

[mu38&Bg#]

It was a bad day yesterday. I scrapped a small part milling a thread. Then trying to figure out why center wasn't on center, I crashed a thread mill. I was fairly upset about the 60USD tool I wrecked and the delay it was going to cause on a paying job until I can get one in. I ran a different part on the mill and noticed the finish wasn't quite right. You guessed it, the spindle now has a runout of .001". Boy was I furious. I do have another collet extension like the one I used and will rebuild it. Hopefully, the cone on the shaft comes off and I don't have to make a new one. If I had the means I'd regrind the ER taper, but it would still be bent. I guess the collet extensions are fairly weak. I'll probably never use a 3/8" endmill in this spindle but crashing one would be sure death for the spindle.

If I was doing it again I'd design for less overhang past the bearings. I was a little worried about it, but am still surprised it bent. I might even use a larger diameter shaft at 25mm and the next lighter bearing will have the same 42mm OD. But, if I was going to build an entirely new spindle, it would have an automatic tool release to allow for quick change tools and the tool length offsets. That probably won't happen anytime soon.

Greg

 

[petertha]

Ouch. Sorry to hear that Greg. Problems are never welcome. But they seem to have an uncanny habit of showing up uninvited particularly when least convenient. I think we can all relate. Well, I know whatever you come up with will be better yet!

 

[Florian]

Hey Greg

Thats a Pity!

But:
Why dont you make your own spindle, get it hardened (that's not expensive) and finally have it ground to size?

Of course its more expensive than getting a new straight shaft but with all the time you have spent, i would say it is worth it. Maybe someone here on this Forum could grind it for you for a better price than if its made by a company (which has to pay employees and all the other stuff...)

Cheers Florian