[RICHARD ZASTROW]

I know back in the day G&L HBM spindles were nitrided. They were suspended vertically in a nitriding chamber that was installed in hole in the floor. I was told it was 75 ft. deep to allow long box way sections to be nitrided vertically as well.

The hardened box ways were installed in scraped cast iron machine frames then bolted in place. That's why they were called "replaceable hardened ways".

Dick Z

[mactec54]

philbur
Have you considered the risk of distortion caused by nitriding.

You don't get distortion when nitriding



Nitriding will work very well for a spindle, as long as the base metal has a good hardness to start with

You don't get any distortion with machining prehard stress relieved material, which are ideal for nitriding


Chrisjh
Make sure that all machined edges have either a chamfer or radius, a radius is best, sharp edges are not good for Nitriding
they must be all smooth, even a chamfer will have sharp edges that need to be made smooth, before Nitriding

[philbur]

Interesting, do you have any links/references.

If it's already hard to start with doesn't he really need to nitride his low cost DIY spindle.

Phil

[ihavenofish]

Interesting, do you have any links/references.

If it's already hard to start with doesn't he really need to nitride his low cost DIY spindle.

Phil

the 4140 htsr should be hrc 32 range. hard enough for everything but the taper in a low power spindle. if he nitrides only the inside taper, it should not pose much warping risk. the taper will need to be ground or hit with a ceramic cutter, and thats about it.

[mactec54]

philbur
Interesting, do you have any links/references.

The nitriding puts a hard skin on the surface, Just like when you Anodize aluminum you get a hard surface, This is not as thick as case hardening but will give a longer life on the taper

As for references, I'm sure there is plenty if you do a Google search, I my self Have had hundreds of parts Nitrided, mostly slides, but some spindle parts

You can see one of my spindle builds here, This is smaller than this project, But I do make them up to a 30 taper
http://www.cnczone.com/forums/cnc_wo...dle_build.html

[Chrisjh]

Hi Mactec,

Thanks for your advice re radii on edges. I appreciate the "voice of experience". I will incorporate a radius on the leading edge of the taper.

The link to your ER Collet design is inspiring. This has given me another idea. I have a lot of ER32 collets. Does your design have a method of locking the spindle for collet changes?

Regards

Chrisjh

[Chrisjh]

Hi Mactec,

Just realized that my question regarding spindle lock was silly. All you need is 2 spanners.

Regards

Chrisjh

[mactec54]

Chrisjh

Yes 2 spanners/wrenches are best for the ER type spindles, the less you have to do to the spindle, the better to keep it in balance, Doing a notch or a hole for a pin is not good, unless everything is symmetrical

The reason I added the extra flats on the ER collet holder, was to keep it symmetrical for better balance

You are on the right track now with your spindle build

[handlewanker]

Hi all, regarding the nitriding,(which is done on a FINISHED part after grinding) the requirements (as far as I know), are that the material must have sufficient nickel and chromium in the alloy to react with the Amonia vapour in a low temperature oven (approx 150 deg C) used to convert the Chromium and Nickel in the surface of the base material to nitrides, and this is done at a relatively low temperature..... but I could be totally wrong on that one.....long time since retirement when that process was done all the time, but the information in the Machinerys Handbook on nitriding also states that it is not suitable for materials like mild steel due to the absence of Nickel and Chromium.

Now that's an interesting point......and if'n I've got it right, you should be able to surface harden stainless steel to make more durable non rusting tools etc.

This could be a simple process for a DIY set-up, as the furnace is low temperature, (around 150 deg C) relatively simple and the gas is Amonia, but providing the material to be "case hardened" or nitrided has enough Cromium and Nickel, and 4140 has that.

It's a bit of an eye opener to see the spindle build by Mactec and realise how thorough you have to be, not only with the machining, but also on the selection of materials.

I think I'll go back to my mill and do a check on the ER32 chuck and collet set I bought on Ebay...especially on the runout check.......the chuck came from a Chinese supplier and looks so nice and shiny with all the blacking and bright shiny grinding areas......it just looks top notch......but having just bought a Vertex BS1 dividing head (Taiwanese make) that also was so nice and shiny, I'm now going to be more carefull.

Chrisjh, could you give us the name of the firm doing the heat treating you mentioned previously?
Ian.

[Chrisjh]

Hi Ian,

The company is Sutton (as in Sutton drills and milling cutters).

They have a surface treatment division which does external jobs as well as their internal jobs. I spoke with Steve Downey.

The process is plasma nitriding, not to be confused with other nitriding processes.

Invented by Germans years ago but only recently taken up by industry when they realized the benefits. The process takes place under low (less than atmospheric) pressure (not a vacuum) in the presence of Nitrogen.

Regards

Chrisjh

[handlewanker]

Hi Chris, thanks for that, I might soon have a number of projects that work better in the hardened state...a quick change tool post and after many years a spindle for a mill I bought 30 years ago...finally got a round tuit to get going....LOL.

BTW, would you have their adress handy?
Ian.

[bru102]

Hi ChrisJH. Interesting thread. A couple of thoughts...

1. Your early posts sent me to Nachi's catalog to understand the Double Row's capability... It was tough to find anything on axial play. I did come across a selection guide that showed them as low in accuracy and high in noise, where the single rows were just the opposite...see image below. So you made a good call on using the paired singles if low axial play is important.

2. Your design should be very good under thermal stresses with the preloaded bearings so close together. I may have missed an earlier discussion, but wondered if you considered a simpler 2 bearing approach with the pair split between the top and bottom of the spindle assembly. That's what Joe Martin (Sherline) does for his line of small machines and "industrial" spindles. Everything I read suggests he has done well with these. They run up to 10k RPM, albeit with small tools and loads. And they have aluminum housings and steel spindles...go figure from a thermal expansion standpoint. A picture follows.

3. I noticed a lot of comments about finding clearance specs but no preload specs. I got intrigued by this stuff a while back...In my "studies and calculations" clearance IS the spec. Positive axial clearance is PLAY and Negative axial clearance is PRELOAD. At zero clearance, their is no play (no backlash). But add a pound of upforce (drilling or milling) and you start to get play. Add 200 lbs of drilling force and you get a bunch of play. So preload means you actually push the balls into the races, deforming things...negative clearance. As long as you stay within specs, that is elastic deformation...the metal springs back. You can find specs and graphs (at least for the single row AC bearings) that tell you how much clearance change (axial movement) you get with each pound of axial force. Complex charts...buts thats the only way I've found to understand what a bearing pair will do under load. If your forces stay within the preload range, you get very little play, because the hardened steel is a very stiff spring. And if you push 400 lbs on a 1" drill bit...you are well past preload, but probably don't care if the hole is .001" too shallow!

[handlewanker]

Hi, I think the axiom that "you don't know what it will do 'til you push it to the limit" would apply to all situations where a simplistic approach is used, as in the Sherline bearing set-up you mentioned.

Most times the simplest design will yield the most reliable results as needed, provided the maximum capabliity of the actual bearings isn't exceeded.

My bicycle has this bearing layout in the pedal department, steering column and in both wheels, and works perfectly well.....and I reckon I'd have to do over a couple of hundred miles per hour before the bearings got hot and bothered.....LOL.
Ian.

[handlewanker]

BTW, the bearing inadequacy will manifest itself when you exceed the capability of the bearing layout to resist the load, or overcome the inadequate preload.

The spindle between two angular contact bearings, lightly loaded, will run freely and appear to be stable, but if'n the load axially or radially causes the bearings to heat up and also the spindle, and the preload slackens off so that the spindle starts to wander in it's plane, then that's when you realise there's more to the design than just two bearings clamped on a piece of steel bar.
Ian.

[bru102]

Hey Handle... good points in both posts. Simple is often a very workable solution. But sometimes robust is the right answer. The sherline approach seems to work superbly for small machines with light loads. The dissimilar metals would be a bad choice in an R8 class machine, but isn't it typical to have a long space between the AC bearings in an R8 setup? The Tormach spindle setup is shown below.

[ihavenofish]

Hey Handle... good points in both posts. Simple is often a very workable solution. But sometimes robust is the right answer. The sherline approach seems to work superbly for small machines with light loads. The dissimilar metals would be a bad choice in an R8 class machine, but isn't it typical to have a long space between the AC bearings in an R8 setup? The Tormach spindle setup is shown below.

most chinese machines have either and AC bearing or a tapered roller at the nose, and an ac at the rear, preloaded with a double lock nut.

this works well. having the 2 opposing bearings locked at the nose, and a free tail bearing (or 2) i think is and improvement on the design, and one that doesnt have to add complexity.

this design is less impacted by imperfect alignment, thermal expansion, and flex i the spindle shaft and adds radial strength and stiffness to the nose.

[Villacherman]

I think I saw it mentioned here in posts before (though my mind gets a little confused reading so many posts), but why is R8 the goal... Why not just use a straight shanked ERXX collet chuck and mount that in your bearing housing?

I believe I'm the intended target audience/client of the original thread author and this seems easier for me... Just curious if I'm overlooking something.

I was just planning on using 2 AC bearings on front and 1 AC bearing on the back. Mounting it all in a steel housing, applying load by clamping the whole thing between the collet chuck head and two lock nuts on the back of the spindle...

Just my thoughts, I like simple.

Adam

[handlewanker]

HI, my two bob's worth......the R8 collet system is widely used and relatively simple in concept, and as it is only one collet per size by itself tightened by the draw bar.....the machine spindle nose is the chuck that holds the collet...... it's also cheaper than the ER system which requires a nose cap as well as a collet chuck and a collet, and has to have the machine spindle with the required interface to accept it..... IE a spindle nose that has a taper to accept a shank with ISO40, ISO30, Morse taper 2, 3, 4 or more etc, whereas the R8 goes directly into the spindle end....no stick out as with a chuck type, so you gain an extra 60mm or so in height to the job.

Having less material in the R8 collet also means you get better vibration resistance and balance.

Limiting yourself to an ER collet spindle end/insert means you're also are stuck when other tools are needed to interface, and a straight shank here is the only answer.

Having an ER spindle nose means you would have to have a complete set of ER collets, not just the few that are needed to mount endmills and slot drills, and unscrewing and dismounting a collet from the nose cap frequently between drill sizes will drive you bonkers in a short time, unless you had a whole load of nose caps to have the collets ready mounted for insertion of the drills etc.

I personally love the ER system, and have an ISO 40 spindle taper in my AJAX mill with an ER32 chuck, so an ER collet chuck was just the best tool holder in that system, it could also have been an Autolock type chuck......and I have an Autolock chuck with an ISO 30 shank which I bought cheap at an auction....but will probably sell it on Ebay.
Ian.

[Villacherman]

Ian-

Thanks for your thoughts, I haven't had all that many hours on mills yet, I've been a lathe guy most my life (10 years) but I'm an engineer, not a machinist! So I get sideways looks when I'm in the shop.

I'm going to ponder yet more.

Adam

[henisrainm]

Good post! I heard that its very easy to remove the spindle without potentially damaging the bearings. How could we do that, could any one guide me? Thanks in advance.

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