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Ross77
01-08-2010, 07:15 PM
So Iím looking at designing the spindle for my machine but Iím not sure of the best way to go.:rolleyes:

Ideally I need it to able to machine wood and metal so high speed and high load will be needed. I have considered just fitting an interchangeable plate on the z axis to fit a router when needed but I would rather use a 3 phase motor and VFD so I can control the RPM, which means a separate spindle is required.

I bought the Spindle book from the Workshop series which covers small tool post grinders for Lathes. For the spindles in the book it says that Ďanyí type of bearing is suitable, even deep groove ones, but for higher loads then use Tapered rollers Bís ( I presume because of the relatively low grinding and milling speed required by a lathe). However after looking at the data from the Bearing manufactures and other peoples spindles then they use Angular contact bearings for the high speed designs.

The biggest problem I seem to be facing is that spindle design is basically a compromise to make it fit for purpose, if space is limited and the tool holder is big then it will require a different layout to say a integral motor design so Iím not keen to just copy a design without understanding why.
At the moment Iím only looking at what bearings to use and the mounting arrangement so the basic design parameters are

1. High load (milling)
2. High speed (routing)
3. ER 32 collet holder
4. Belt driven or end mounted motor

So has anybody made something like this or used normal bearings in a spindle?

Im initially looking an somting like the ones below from SKF web site, but I might be aiming a bit high :smile:

http://www.skf.com/portal/skf/home/products?lang=en&maincatalogue=1&newlink=9_10_8

http://www.skf.com/images/cat/images/9/9_0/6002_p52_2.jpg
http://www.skf.com/images/cat/images/9/9_10/6810_p12_2.jpg

routercnc
01-08-2010, 09:12 PM
Hi Ross,

Ambitious!

On this site they suggest bearing choice is down to the application, so no definitive 'right answer'. Ceramic bearings are sometimes used (silicon nitride).
http://www.spindleservices.co.uk/Spindle_Services_design.htm

Can you machine it to hold the tight runout a spindle often has?

What are you thinking of for balancing? Do you think building it all up and sending it off for balancing would be an option? Or do you think offsite individual part balancing, followed by offsite assembly balancing would be required?

I went for the 3 phase and VFD option for the reasons you mention, plus nice and quiet!

Here's another bit of info. Mentions bearing specs . . .
http://henriksplace.se/cnc/new_machine_bt30_spindle.html

And for bearing pre-load:
http://machinedesign.com/article/how-retaining-forces-affect-spindle-bearings-0919

One from the skf magazine:
http://evolution.skf.com/zino.aspx?articleID=20

Best of luck . . .

routercnc
01-08-2010, 11:25 PM
On second thoughts, maybe start with a die grinder as 2e0poz suggested in another post . . .

Ross77
02-08-2010, 01:10 AM
Thanks Barry.

Theres some good links that i didn't find, Thats why I like this forum...:beer:

I did see the Henriksplace one and In all reality, design wise, thats what I will end up with, minus the hardening and grinding bit.


What are you thinking of for balancing? Do you think building it all up and sending it off for balancing would be an option? Or do you think offsite individual part balancing, followed by offsite assembly balancing would be required?

to be honest I hadn't thought about that, do you think it will that much of an issue? after all it i will be fairly small diameter stuff machined in one operation( if I can sus it out)



Can you machine it to hold the tight run out a spindle often has?
Probably not but I have plenty of AL stock and cheap bearings to practice on. and I'm willing to learn, if my lathe will let me.:smile:



I went for the 3 phase and VFD option for the reasons you mention, plus nice and quiet!


Probably another post in it self but what is the max speed you can get before its to noisy? Have you geared it?


On second thoughts, maybe start with a die grinder as 2e0poz suggested in another post . . .

Yeah I have concidered that as apparently they have a double A/C bearing in the nose but having looked at this site

http://www.cncathome.com/spindles.html

he reckons that they are are just up rated routers so the noise is a problem, but i would like to know if anyone has had any success with them?

GeorgeD
02-08-2010, 01:23 AM
Whats wrong with an induction motor being used?

This one I have is heavy and I reckon its the motors body thats the bulk of the weight?

GeorgeD
02-08-2010, 01:28 AM
lol that vid is awsome,I do like his tool changer method :clap:

Ross77
02-08-2010, 01:43 AM
Hi George

As you stated induction motors are heavy (not good on a z axis) and I believe are difficult to control the speed. :nope:

The idea of using a 3 phase motor and Variable Frequency Drive (VFD) is that you feed it 240v AC at a set current and control the speed by "varing" the frequency of the AC supply. Therefore you get full (ish) power over the whole speed range. not to mention over speeding the motor to way beyond its rated speed if you dare........:eek:

I'm by no means an expert on this so I plan to post a separate question on motors later if your interested?

GeorgeD
02-08-2010, 01:55 AM
Just use a 750wLight dimmer. lollol

John S
02-08-2010, 02:31 AM
Just use a 750wLight dimmer. lollol

That's a bright idea.

Ross77
02-08-2010, 03:07 AM
Just use a 750wLight dimmer. lollol
Thanks thats really usefull (dont know why I bothered posting, 10 replies and only 2/3 serious ones)

GeorgeD
02-08-2010, 03:32 AM
Lighten up,Ross...I was only jesting. :wink:

routercnc
02-08-2010, 11:30 PM
Hi Ross,

I asked about balance because the spindle I bought had balance holes in the collet nut. It's another step towards a more refined and accurate machine.

The material you were researching is from manufacturers who make machines which run all day, and under a high workload. They are always pushing the boundaries of what is possible, and charging £1000's for them. Maybe you're beating yourself up a bit there with what you might achieve, but bravo for giving it a go.

I've yet to run my machine yet (hobby on back burner for now) but similar machines on the internet spin up nicely to 24,000rpm and I'm expecting the same. No it's not geared - I suspect it is like the section view I posted a while back.

This is the machine I bought:
http://cgi.ebay.co.uk/1-5KW-WATER-COOLED-SPINDLE-MOTOR-ENGRAVING-MILL-GRIND-/230498631924?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item35aaca00f4

Sorry, this is the blind leading the blind unless some has actually done this . . .

Ross77
03-08-2010, 01:20 AM
Lighten up,Ross...I was only jesting. :wink: I know. how about this??


Sorry, this is the blind leading the blind unless some has actually done this . .

Thanks Steve....... I Wonder if I will ever get this working..:smile::smile::smile:



I asked about balance because the spindle I bought had balance holes in the collet nut. It's another step towards a more refined and accurate machine.

Not the dreaded vibration stuff again :naughty: there is a version in my mind that inverts the motor so it is parallel to the spindle and mounted the opposite side of the y axis gantry but running the opposite way to the spindle to cancel out the inertia (not sure of the terminology)........



Maybe you're beating yourself up a bit there with what you might achieve,


yeah I'm under no illusion that I can make a super accurate precision spindle that can run 24/7, but I would like to have a fighting chance of making a decent home use one.

I've been looking at the A/C bearings and there are so many to choose from with different angles and precision ratings, I can get a budget one for around £12 but the proper matched pairs can be around £100 or more. I just need to work out if using good bearings will average out my machining skills or if they are a waste of money at the moment.

I can see my self just getting the cheap ones and a few deep groove ones and then just trial and error... if the run out is acceptable and it doesn't flex or chatter when cutting then job done :smile:

GeorgeD
03-08-2010, 04:05 AM
To be honest with you here Ross...I would rather go and buy one of those Chinese spindles on ebay,just seen one for £130 or nearest offer.

Your taking this to the extreme by worrying about precision from the motor and its housed bearings arrangement,too much headache.

Whats your goal in the CNC ie what do you want to achieve in terms of product?

routercnc
03-08-2010, 08:42 AM
George,
Some of Ross's goal is hinted at in post#1.

Ross,
I wonder if you need to break this down a bit. Maybe convert a big old mill to cnc for the lower speed, big roughing out work in Ali, and concentrate on making a high speed VFD controlled spindle (20,000 - 30,000 rpm) for the gentle stuff and the routing in wood.

Taking a punt, several of the Chinese spindle boast 'imported bearings' or similar, so maybe they suffered early on from the cheap ones. I'll stick my neck out then and say go for the £100 A/C combo, plus a cheaper ball bearing at the other end.

As for the drive, I think that even with the parallel mounting idea, unless they are out of balance by the same amount, and the oob is in the same place radially, you'll not improve things.

Ross77
03-08-2010, 06:27 PM
To be honest with you here Ross...I would rather go and buy one of those Chinese spindles on ebay,just seen one for £130 or nearest offer.



Yes but I want a ER 32 collet and 8000rpm is still to fast for milling. its also part of a whole one piece Z axis that I'm trying to design.


Your taking this to the extreme by worrying about precision from the motor and its housed bearings arrangement,too much headache.

Well its my hobby and I like to do things properly. I what to learn how to machine accurately so If nothing else it will be a learning exercise.



I wonder if you need to break this down a bit. Maybe convert a big old mill to cnc for the lower speed, big roughing out work in Ali, and concentrate on making a high speed VFD controlled spindle (20,000 - 30,000 rpm) for the gentle stuff and the routing in wood.


Yeah I'm coming to that conclusion. Although not with two machines (I'm not made of money...) but with a cartridge type spindle that can be swapped for different jobs, A/C for high speed and taper bearings for high load.


From what I've found the problem seems to Lay with heat.....

For high load you need a high contact angle 40 deg or more and therefore more friction, and heat but for high speed you need the opposite, a low contact angle (15 to 25deg. seems to be the favorite) which reduces the heat but also the load capacity. so therefore it would seem you cant have both (Unless any one knows different?)

The heat also affects the preload which in turn affects rigidity. for high speed you need a variable spring loaded one but the most rigid is the fixed permanent type

Hence "Mills for milling and routers for routing", but at least I now know why :heehee:

Anyway this should really simplify the design and manufacture of the separate spindles

GeorgeD
04-08-2010, 11:38 PM
Are those motors that poweful?

I know when I messed about with RC fuel powered model engines,these type of motors were not known back then.

The little bee engine I bought I affixed it to a piece of wood and the darn thing took flight towards the ceiling and bored a hole in the ceiling.

sorry for the ramble.

Ross77
05-08-2010, 12:05 AM
Wrong thread George you want The "hope it'll cut Ali" one :smile:

Back to the bearings I have found an excellent company called Bardens and the catalog is full of bearing usage and design guides but in nice easy to understand format. The big upside is that they have a UK branch just down the road from me, but I expect they will be mega bucks and wont deal direct with a small time hobbyist. Still nothing ventured nothing gained.

Heres the catalog if any ones interested http://www.bardenbearings.co.uk/c2/uploads/barden%20uk%20cat.pdf

Theres also some precision bulletins that deal with effects of high speed and using smaller lower mass balls to counter effects, scroll down the page a bit.

http://www.bardenbearings.com/literatr.htm

So maybe I can build just one spindle after all :smile:

GeorgeD
05-08-2010, 12:13 AM
lol sorry about that Ross.

GeorgeD
06-08-2010, 02:12 PM
I mentioned in one of my post about the use of a Treadmill motor,these are slim and 118v? to run it we'd need a dropper supply....hmmmm,ain't microwave power supplys 240v primary and 118v secondry. :wink:

Tom
06-08-2010, 05:54 PM
hmmmm,ain't microwave power supplys 240v primary and 118v secondry. :wink:

George, please be careful to electrocute yourself...
Anyway, back on topic...

Ross77
06-08-2010, 06:49 PM
Thanks for the input George but I dont really need to sort a motor,

I already have plenty of 3 phase motors and a VFD, This also isnt a budget build. What I'm trying to work out is far to go without over doing it on the spindle and bearing side.:smile:

Anyway I think I have decided on the layout and bearing configuration so I will post some drawings soon.

Then I will need some advice on the best way to actually make it. turning between centres and line boring etc.

GeorgeD
06-08-2010, 07:03 PM
George, please be careful to electrocute yourself...
Anyway, back on topic...Old fart...why'd you think I know its 118v at the output. :tongue: