Milling spindle collaboration project

[pstockley]

I have been looking everywhere for a milling spindle to use on a future project. My requirements are:

1/ Support about 2.5 to 3 hp
2/ Have a 30 NMTB taper
3/ Run to 8000rpm
4/ Have class 7 class bearings

Setco have something that fits the bill (Sentry ) but it is $2980 dollars. This is just too much to justify.

Would anybody be interested in collaborating in the design and manufacture of a general purpose spindle and share in the development costs. I was thinking of something along the lines of:

1/ Support up to 3hp

2/ Have the option of a R8 or 30 NMTB taper

3/ Support class 7 class bearings or lower class ones for people who want a reduced cost.

4/ Support a powered draw bar (in the future)

5/ Designed for belt drive

Anyone interested?

[andy55]

the problems with standards is that there are so many to choose from ! my friend and I are toying with the idea of making a spindle and we were thinking SK40 taper, definitely with a pneumatic gripper drawbar (anyone know what typical forces for these are?)

could you expand on the bearing reuirements ? what are the specs for class 7 bearings ?

belt drive sounds OK, maybe with two wheels for two speed ranges (with 3000rpm motor we would have 1:1 and 1:2 for max 6000rpm)

[NC Cams]

Frankly and with all due respect for your creativity, your specs are inadequate to spec out the bearings for such a spindle.

As soon as you talk 8000 rpm, your putting yourself into a tough area (engineering wise) so as to come up with a bearing that will support the loads and the speeds, not to mention lube and preload and fit them.

You can easily transmit 3hp thru a shaft with little concern over the bearings - until you start to apply combined radial, axial or combined radial loads to the bearings. Thus, you start having to pay more cash for speed and more for radial capacilty as size and speed go up.

Small size bearings are competitively priced (IE: 6203's) as everybody makes them like aspirin and there are jillions to choose from. Bigger bearings and/or ABEC 7's are scarcer and not so widely made thus they command and get a higher prices. Classic law of supply and demand.

Re: the cost factor, check out the cost of ABEC 7 bearings regardless of size. Depending on the size and configuration (duplex, triplex, quad, roller,etc) you can easily tie up $1-2K in bearings alone.

For grins, check out the price of a set of 7207CTYDUMP4's (duplex, abec 7, 207 size) for the nose and 6206VVP4 would probably work as a guestimate at the other end of a mill spindle.

Compared these to the $$$ for regular 6207's and 6206's and you'll see why spindles are so pricey.

THen figure what it will cost to machine, heat treat and OD and ID grind the shaft afterwards. Don't forget the housing maching and ID grinding (to tolerances of 0.0001 or better).

Unless you have the machinery (OD, ID grinders, lathes, mills, etc in house already) that is capable of doing it, you'll be talking a small fortune to have it done by a job shop.

Yes, it would be nice to find an ABEC 7 equipped spindle that would do what you want for much less than $2900. Chances are, houweve, that it have already been done if it were financially feasibile/possible. Or one would be on the market from Taiwan or the ROC. In today's price sensitive market, people would be beating a path to your door for one - again if it were possible.

Re bearing specs: get a hold of a bearing catalog from any precision machine tool bearing supplier. Most show the specs for ABEC 7 (same as ISO P4). NSK's catalog #E124 has them on page`A8 thur A10. Spindle and housing machining specs are found in same catalog on pages A15 thru A17. Same catalog shows other stuff you'll need to know/apply if you still intend to make a spindle on your own.

I wish you well in your endeavors....

When you see the numbers you realy should be holding, you'll see why the $2900 price for a precision spindle from stock is really pretty cheap....

[andy55]

anyone know of sources for hobby-level spindles with standard tapers used in cnc machines ?

I found an MK3 spindle at littlemachineshop, but it's a bit small:
http://www.littlemachineshop.com/pro...ProductID=1508

ISO/BT40 size or similar would be nice. preferably one that fits a pneutic gripper.

Since it's apparently really hard to make the spindle DIY I'm thinking that fitting the bearings and the holders for the bearings + spindle box can be done DIY.

[pstockley]

NC, Thanks for the frank reply. I understand this is far from a trivial exercise. I have being doing a bunch of research and have read most of the bearing manufactures literature. I knew going into this that the bearings cost a fortune.

I have a CNC mill, a Myford super7, a hardinge TFB and a Dunmore toolpost grinder. A long time ago I built a grinding spindle just using a Myford and toolpost grinder. It certainly was an exercise and with a certain amount of luck actually turned out pretty good (around 0.00015” run out, that I could measure) and was capable of grinding at 15,000rpm using a 3/4hp motor. However, it took a long time to make and I wouldn’t fancy my chances at being able to replicate this feat with any certainty of success.

To get the cost down, I am thinking I will have to get a bit creative. I have looked into the availability of existing R8 spindles (minus housing and bearings). I have decided to buy the spindle from a Grizzly G3102 small Bridgeport type mill. This claims to have ABEC7 bearings as standard so hopefully the tolerances on the shaft should be OK. They are asking $160 for it so it’s worth the risk. I don’t like their housing or bearing setup so will design my own. There are some local precision grinding shops I am going to talk to about doing the ID grinding on the bearing seats. For my first attempt I may fit ABEC5 bearings as they will be good enough for my initial requirements. Based on the spindle design I think it should be ok for about 1 1/2hp under typical hobby type milling conditions. The important aspect for me is rpm capabilities of at least of 7000rpm as I plan to use it with small end mills mainly.

Andy, I plan on fitting a power drawbar similar to Power Drawbar

I will probably use either R8 tooling or Tormach tooling holders (TTS) I use on my
CNC mill.

The spindle is backordered so I probably won’t get it for 5 or 6 weeks. While I waitI will start drawing up some design ideas.

[NC Cams]

There are several philosophies to consider:

Make a precisiong spindle, use precision bearings, assemble it and grind the ID to get the axis of the spindle to run tru to the axis established by the bearings.

or

Make semi precision spindle, use semi precision bearings, selectively assemble (move them around until you get axis to run true) then "lock it down" and grind the ID.

Make whatever for a spindle, use whatever for bearings, grind after selective fit but don't be surprised if you end up with something that is oversize and doesn't holed tolerance.

Whenever you talk high speed, you want the cutter running true. Otherwise, finish, chatter and size control become concurrent problems. Thus, precision machining and bearings become more critical as speeds mount. Like we tell our racing customers, "Speed costs money - how fast do you want to go and how long do you want to go that fast???"

I bought an import mill and it ran well as is. Since I worked for a bearings supplier, I figured I"d "tune it up" with some surplus ABEC7's that were being tossed.

Result: Disaster

Reason: the housing and spindle were selectively fit (cheap labor enables you to assemble/reassemble sloppy stuff until you get it to work much cheaper than buying expensive bearings and holding tite tolerances when grinding).

Yes, you can buy the spindle as a "core" and then via grinding, plating and selective fitting, you can blueprint the part to do what you want. However, it will cost time and/or money. Do you have either/both to spare????

[Enraged]

andy, did you see this: http://www.littlemachineshop.com/pro...ProductID=1407

an R8 spindle for the mini mill.

can anyone tell me where I could look for bearing that would be suitable for use with this spindle? I found a seller on ebay, VXB Bearings I think it was, that has a very large amount of auctions for various bearings, so I was looking for a relatively low cost alternative.

[NC Cams]

Low cost and machine tool grade (ABEC 7 or ISO P4) bearings are an oxymoron.

IF you want to do high speed grinding, ABEC 7 bearings make a huge difference with regard to size control and finish. How so???

A straight drill will drill a precise hole but a bent on will wobble and cut a funky hole.

Generally speaking ABEC7's have HALF the runouts an a fraction of the tolerance of ABEC 1's or 3's (typical "electric motor" quality bearings). They are priced accordingly UNLESS somebody is blowing them out to get their money back because they were stuck with them.

From my experience in the bearing industry, any quality bearing supplier will gladly provide an inspection dwg that "certifies" the fact that you'd be getting what you pay for.

If someone says, "trust me they are ABEC 7's" , don't unless they'll provide certs. See prior post on how to selectively use/fit lower spec bearings and spindle for low net spindle runout.

In short, you'll pay for it in time or labor but high running accuracy costs.....

[Enraged]

i am just in the process of building a small benchtop cnc mill. nothing spectacular, it is primarily a school project (taking mech engineering technology right now), but i am using good quality parts such as ballscrews and precision ground shafting.

[gbowne1]

My requirements for a spindle of such type would be:

NMTB #40 40mm taper
up to 3,000 max RPM
down to 275 min RPM
belt driven by NEMA motor @ 1,750 motor rpm
belt is a (much wider than automotive type) serpentine belt style.
capable of at least 4" Z travel
precision to 0.001 to 0001 better.
Uses ABEC 7's.

Never seen any reasonable cost 2 to 5HP motors, not even 3's in NEMA enclosures. Anyone have good Baldor part #'s?

I wont have a tool changer.

I thought about CAT 45 but holders take up too much room and I already have a whole pile of NMTB 40 taper holders.

would like it to support FANUC 6 series spindle drives & servos as I've got them already

don't really need the power drawbar but the downfeed

I'd love some help in this respective too myself.

private comments can go to gbowne1@yahoo.com if you want.

[JFettig]

I am personally looking into making a NMTB #30 spindle for up to about 5000rpm or so(more if I can get the bearings) for my next mill project.

These tool holders use a simiar drawbar and similar power drawbar like what you see on bridgeports right?
I have one of those half built that I would like to complete and would probably work well on this type of setup.
I was origionally looking at a retention nob tool holder setup, but that requires high pressure on the spindle bearings and a high pressure large air cylinder and all.

Jon

[gbowne1]

Yeah, those require the 5/8" threaded drawbar like you see on bridgeports. I think I remember seeing bridgeport-type mills w/either 30 taper or 40 taper, but I don't like the design of the head.

I've got so many NMTB #40 40mm taper tooling (most of them Weldon brand)
that it is relatively economically sound for me to use the NMTB #40 taper. I thought about using the CAT45 taper tooling which I have only a few of. (Came with some other NMTB tooling I got at an auction) but it's not what I like. Though there is the possiblity I could change the spindle out later, and add an ATC.

I'd love to find a decent sized belt and NEMA frame motor to use. Anyone got any suggestions? V-Belts don't appeal to me, even though I've seen them cheap.

Anyhow, there's always a possibility out there somewhere.