fretting on 30 taper tooling

[2ferrous]

I've noticed recently that my BT30 tooling has been showing signs of fretting on the taper. I'm not sure if this is because of increased production/use or because I've been more aggressive with the tooling. My favorite end mill is the IMCO 1/2" 2 flute streaker which, depending on the program, could be cutting up to 0.5" depth and full width through 6061-T6 aluminum. The spindle barely even loads up and the DM4400 seems to not even notice. Tool holders with drills or boring heads show no sign of this whatsoever, just the end mill holders.

Perhaps the Belleville washers are getting weak...

Is this happening to anyone else?

Timothy

[UWP_Wes]

Tool holders are consumable just like any other kind of tooling. On a long enough time line, all tool holders will have the same problem. You need to replace them from time to time, just like pull studs.

If it concerns you, toss them in the scrap bin and get new ones. Loose bellvilles could be part of it. A 30 taper has less bearing surface than a larger taper, so they will wear faster. If the fretting gets too bad, I suppose it could even damage the taper in your spindle.

-Wes

[2ferrous]

I have a pretty good mix of new and used holders, but I have noticed that most of the fretting is with the 'Command' brand of holders. I have some Kennametal and Sandvik stuff too and they seem alright.

When I bought the machine it had been sitting in a garage for the last 10 years because the owner couldn't get it running, and it still had a tool holder in the spindle. So, thats 10 years with the Belleville washers in the semi compressed state. I have a feeling that they may need to be replaced. I'm just not thrilled about removing the assembly and sending it out for repair.

I should buy one of those draw bar testers...

Clamprite - The most economical tool for checking spindle drawbar pressure

Timothy

[2ferrous]

I am worried about the spindle. I can't imagine the cost of repairing the taper if it gets buggered up. I'm hoping to fix it now before it gets bad. I'd hate to drop a tool at 6000rpm....

As for the worn tool holders, I was just going to have them reground. There seems to be plenty of clearance for the tool holders to seat further into the spindle.

Timothy

[olfoundryman]

Timothy,
Hullo again, How is the weather in Canada? Loverly sunny 23 deg C day here in Melbourne!
Yes I have had a bit of a problem with fretting too. It seems to occur more towards the smaller end of the taper. It also seemed (I think) to be more noticeable on tooling from Hong Kong, the Swiss stuff (Regofix) did not seem to suffer as much if at all. Anything with strict vertical loading – like a drill or as tap is unlikely to cause fretting - its more, as you have observed, the two flute type cutter that does it worst. I began to notice it when I was machining cast iron. I suspect that 4 flute cutters might do it a little less. Fretting is definitely not a good thing as it slowly tears minute metal particles of the two surfaces involved, these particles immediately oxidise and the “rust” thus created is an abrasive and so the damage worsens. The first thing I did was to take a good look at the taper on the tool. I found a few little Knicks and dints probably made during rough insertion and removal from the spindle - I stoned these off. Also have a very good look at the internal taper as well. The edges on the open end of it can also get damaged by rough insertions /removals - I slightly bevelled mine (just the very edge) with a dremmel and a rubber abrasive “stone”. Also with a mirror have a very good look at the internal taper, at one stage mine had a very flat piece of Al swarf stuck on it, it was stuck quite hard and had to be carefully scrapped off. I had an old piece of BT30 tooling that I don’t use and after having removed the drive dogs from the end of the spindle I use this old tooling as a lap with some very fine abrasive and oil on the internal taper. I did this for just a second or two and then very thoroughly washed the internal taper clean. Another internal inspection followed to check for lumps knicks etc (I did not find any). I clean all tooling every time before insertion with a hard plastic pot scourer, I use the same to clean the spindle taper. I amm very careful both removing and inserting tooling. When using the tool changer I always have the internal air blast operating on the spindle. Also when using the tool changer and the air blast I always lubricate all tapers with WD40 before fitting as a lubricant should help stop the oxidation that is so much a part of fretting. It may also help the tooling pull down a bit tighter.
All of the above does seem to have helped a lot and it may even have stopped the fretting completely – time will tell.
I too got concerned about the Bellville situation. It quite possible that one or more is broken or that the lube on them has dried out and they don’t move as well as they should. I have heard too that the tubes in and on which they run can get damaged enough to restrict movement. You need to check out the relative positions of clamped, unclamped, and clamped with no tool present to get some idea of how far the stack of washers is moving. You want the minimum movement possible between unclamped and clamped (tool present) so that there is max possible “tension” in the washers – this after all it what holds the tool in place. If there is too much movement the washers will be almost back to their “clamped no tool” position in which case there is much less tension pulling the tool into place. Mine was Ok here.
I did look at trying to remove the washer stack for a quick inspect and replace if necessary but there is a little socket head screw right in the top end of the spindle – you have to remove the pressing bar mechanism to see it - that seems to be needed to be undone to get at the washer stack. I could not get it undone (perhaps it’s loctited) so in view of the lack of instructions I gave up. Perhaps someone over there can contact Roberto and ask him how to get the stack out – I have never managed to get an answer from him – it’s an overseas thing I think!
The thought of trying to find someone to regrind the internal taper properly and accurately without having to rebuild the entire spindle fills me with great fear and trepidation. Also the tooling is so cheap – well, relatively - that I would not bother having it reground, just but new stuff
Martin.

[2ferrous]

Hi Martin,

Good to hear from you again. It's currently 4C here with impending snow.
What better reason do you need to hide in the shop and tinker about?

Like yourself I clean all my tool holders on a regular basis and keep a piece of fine scotchbrite handy to wipe off any fretting marks. I've looked closely at the spindle taper and its in fine shape. I also scotchbite the taper once in awhile just to make sure its clean and free of swarf. Still, the fretting continues and I'm convinced that the belleville washers are to blame.

Last week a tool holder actually pulled out of the spindle while running a drilling cycle.

I count myself as super lucky that I was standing there to hit the Emergency Stop before any real damage occurred. I was using a G83 peck drilling with a 0.344in drill and it jammed at the bottom of a hole. When the Z axis lifted up, the holder and drill stayed in the workpiece. I heard a odd click when this happened and as soon as I looked over and saw what was going on, I stopped the machine. The Z axis was on its way down to finish the hole. The carnage would have been unbelievable.

I have a second spindle from my No.1 machine and I'll disassemble it to find out the proper belleveiile washer dimensions and I'll photograph the whole procedure so that others can follow along.

Timothy

[Caprirs]

I have a handful of extra belleville washers from Dyna for my DM4400Ms. Using calipers, these measure:

OD: .784"
ID: .407"
Thickness: .036"
Overall height: .062"

I cannot find in the manuals how many are required or how they are stacked.

[olfoundryman]

Timothy, Capris, Send me some of that 4 deg C please it was about 34 Deg c here today and as my main thing is foundry it's a bit hot - Love those 14 deg c days best.
My dyna manual has a crude cut away section of the spindle and it shows 80 belville washers with the Part number AM 201010 which I would guess means 20 mm Od 10 MM Id and 1 mm thick but the Part number should give it all correctly. Hopefuly I have managed to attach a pic of this section. They appeared to be arranged in pairs with the top pair center high up the next pair center high down and so on. The section is none to clear as to how one would take it apart. There would appear to be some sort of push on cap that the pressing bar pushes on under/ inside which seems to be a couple of threaded bits that screw on the central shaft around which the washers are stacked. At the other end of this shaft is the bit with the balls that grab the tool pull stud. This is threaded on to the shaft but is locked in place with a grub screw which you can not get at without taking the assembly out of the spindle. So it all has to come apart from the top. The little grub screw that gave me such concern is not shown in the section and is right at the top of the shaft. It goes vertically down into, but slightly off centre of the shaft, it seems to be in some sort of large screw driver slit. To me it looks as though the whole stack of washers is under considerable tension (compression) even when in the clamped no tool position. I get the idea that taking it apart could result in washers etc flying all round the room as you undo the last turn of thread. I suggest that you tread with care - check with Roberto if possible. You may need special jigs to hold the washers while it is all taken apart or put back together.
Also I would check to see if is not just simply out of adjustment and therefore only just grabbing the pull stud- where on its gripping taper do the balls mark the pull stud? You can watch how far the arrangement moves by looking in where the belt drive is. From unclamped to clamped tool in position there is some movement - I can measure mine if you like - If there is very little then the balls are probably not geting the right grip on the pull stud, if there is a lot then much of the washer power may be expended before the grip takes place (looking at the stack of washers and how it moves I think this is a bit unlikely even if it moves quite some way). Also are you sure that you have the correct pull stud - stupid question I know - but I have to ask)
Dropping a tool holder sounds like a real bad happening - I dread the thought - and I have a suspicion that you may be right about the washers being bad. It would only take one to be broken or some water to have got in and all gone rusty to creat havoc. its just that I would suggest going in easy rather than "Gung Ho" But please, whatever happens good luck and, please, keep us all advised - I may have to go down the same road!
Martin.
Old foundry men never die they just loose thier sand

[Caprirs]

There is a special tool for taking the drawbar apart and out of the spindle. The drawbar is a two piece design. The tool fits into the spindle taper and locks the bottom "cup" so the top can be loosened. Long ago, Dyna used to lend the tools out but I don't know if they do that anymore.

[2ferrous]

You wouldn't happen to have a part number for this tool would you? I'd be happy to buy one.

Timothy

[Caprirs]

I actually have the tool! No idea what the part number is. I could see if I could sketch it up and maybe you could duplicate it? Pretty simple really.

[2ferrous]

That would be awesome. I'm sure I could make one.

I found belleville washers here

Disc Springs to DIN 2093

Looks like the D201021 is the correct match. I'd like to find out what my conical spring washers look like compared to new ones...

Timothy