Anyone know about shrink fitting tools?

[Engineeringtech]

Hi everyone. Anyone here know about shrink fitting cutters and drillbits into steel shafts?

The other day I needed do drill some very accurately placed, .147" diameter holes in a cast chassis with tall (3") side walls. As some of the holes were located within 3/8" of the side walls, a jobber length drill wouldn't reach without the chuck striking the wall. I had some taper length drillbits, but they weren't split point, and drifted when I tried to start them. I couldn't drill from the bottom side of the chassis, because my reference points were on the inside.

I decided to make a drillbit extension. I had a split point, screw machine length drill in .147" diameter and some 1/2" diameter shafting that ran very true in my lathe. I would drill the end of the shaft to accept the bit, and setscrew it into place. But then I thought I had a better idea. Some companies attach their cutters to tool holders by shrink fitting them. (I've never done it, because all we have is R8 tool holders.) Closest reamer I had was .145". So I drilled a .136" hole, then reamed it to .145" (1" deep). I blew out all the chips, and while the spindle was turning, heated the drilled end of the shaft with a torch. I figured that would prevent the shaft from warping. Once I got the end of the shaft dull red in color, I stopped the spindle, and quickly drove the shank of the .147" drill into the hole using the tailstock chuck. Unfortunately, the shank only penetrated about 1/8" and stopped. It doesn't run very true.

Was the .145" hole just too small? Or should I have heated the shafting more? Or is this just a bad way to make a drillbit extension?

 

[purpleknif]

I'd look into a long ctr, drill and drill bit. Shouldn't cost that much.

 

[goldstar31]

I seem to recall scribbling a few notes about D Bits before going off on part of an extended holiday. Got no response-on my return and thought that no one was interested or I'd got it wrong or was suffering from the dreaded dementure.

Making up D Bits from drill rod or what we call , silver steel will do your job- if you are careful.
Again, the other way is to silver solder( not again, merde) is to drill into the jobbers drills and lengthen them with a thinner rod in the blunt end of the hss drill.

If you think about it, the blunt ends of hss drills are left softer than the sharp ends.
So it is probably a collet job to hold the arse end of the appropriate drill whilst drilling.

I've got a drawer full of extended drills, the hardest part is to avoid the peccadilloes of the silver solder brigade.

 

[MachineTom]

On super high rpm machines end mills and drills are a shrink fit. Your problem was that .002 is to tight a fit for the shrink. Steel expands .000005 per inch per degree F. So if you added 800° X .000005 X .150" = .00006 Now that is the quick and dirty method. As the ration of the diameters is huge it likely expanded more than that. For a piece like you want a fit of -.0005 or closer would work.

If you mic that drill it is smaller than its hole size, that is the number. Reamers can be purchased in most any size. .0005 increments sometimes less

 

[MachineTom]

Rereading the post all you need is a couple of inches. MSC #26 drill 135° split point 6" $3.90 there is also a 12" that you can cut off to whatever. I would suggest that you buy an extended length spotting drill, 1/4 ,5/16 diameter. If you need accurate hole location spot first then drill drill.

Without looking up the price a spotting drill at $20-30 is worth every penny when you need it.

 

[kvom]

I recently had to get a 6" drill and tap for a deep hole. Found both at McMaster.

 

[Swifty]

I seem to recall someone posting on this forum about using loctite to hold the drills in. This way you can drill the hole in the extension to suit the shank size, work your way up with smaller drills until the shank fits in. You will be able to remove the drill by applying a bit of heat.

Paul.

 

[goldstar31]

Paul,
Unfortunately Loctite isn't one thing. Maybe someone else can describe one product that works in the probably hot, hurly burly of drilling.

My experience is that my D Bits run so hot that drilling long runs in -say lignum or rosewood blackens. In addition, I have known silver steel bits lose their temper. If you think about it, quite a lot of gunbarrel reamers are force fed with coolant.

Me, I'll stick( ooops) with silver solder for my more modest pursuits.

Regards

Norman

 

[Swifty]

Norman, I also have used silver steel silver soldered to the end of a drill, just have to be careful aligning them when soldering.

But the main problem still exists, how do you stop the drill from wandering if the part is not centre drilled first. An accurate centre punch may suffice. The original poster wanted to drill cast parts, so I think some sort of centre spot is advised, maybe it will be possible to use some sort of guide with the correct hole size in it, held in position where the hole needs to be.

Paul.

 

[goldstar31]

Paul,
Long answer- and maybe a rambling one. Old age and that!
The first point is why a long series of drill or an extended long series of drill to drill a hole of perhaps less than an inch. Take a serious look at your intended tool and you will find that the metal which gives it rigidity - or should, isn't there. Somebody removed a whole spiral of the stuff- before you got it. So if you are drilling a shallow hole- you need a long twist drill- like a hole in the head.

Again, I assume that the part to be drilled is a casting. Is a casting actually flat? No it is not.
If ANY drill is presented, it will wander on the uneven surface and probably the surface is chilled. Back to the drawing board! So we have get a flat surface( it gets worse on a bit of round) but you need an end mill. Cries of 'Heresy' or worse but wandering drills are there to annoy.
So you now have a flat surface. You can centre punch it, whatever you are going to follow up with a centre drill to open up a way for the size drill. You don't normally get a centre drill which is long enough to get there before the intended drill. Back to square one!
And when all is said and done you are going to play about with a wobbly twist drill that may have a blunt end or the point in the wrong place.

So why not have a four facet end to your drill instead of this 118 degree double lip affair?
It avoids the centre drill part!

It still leaves a sort of long drill- to wobble and I've long been an advocate of the simple D bit which is easy to make- dead cheap and which can be re-sharpened in a trice. It doesn't require anything but itself and will drill- well 13" dead parallel and to size. Again, it will be stronger than the extended twist drill and so on.

As for a guide- you are right to mention it. I have drilled lots of long holes in the lathe. I assume something similar in the mill or elsewhere but I pull the poppet out of the lathe tailstock and replace it with a dummy one with an accurate hole not a morse taper or a drill chuck and get the tailstock right up to the work spinning in the chuck or face place.
So I may have 13" of drill but only a little bit held firmly to peck drill, clear the chips,peck drill and so on.

I hope that this has been interesting without deprecating. Thank you , Paul, for raising the matter.

Norman

 

[Engineeringtech]

I'd look into a long ctr, drill and drill bit. Shouldn't cost that much.

Available long centerdrills are still too short. At least the ones I have.

 

[Engineeringtech]

Goldstar - I'm not good enough yet to make my own drillbits from scratch. I've resharpened bits (by hand), but not split point bits. And I wouldn't trust them to START a hole. I'm also not sure I would a attach a thinner shank to the jobber drill bit. The thing flexes too much as it is. But I will mull over your suggestions, as I may be missing the point.

 

[Engineeringtech]

Rereading the post all you need is a couple of inches. MSC #26 drill 135° split point 6" $3.90 there is also a 12" that you can cut off to whatever. I would suggest that you buy an extended length spotting drill, 1/4 ,5/16 diameter. If you need accurate hole location spot first then drill drill.

Without looking up the price a spotting drill at $20-30 is worth every penny when you need it.

Thanks. I saw your calculation for the shrink fit. I was over estimating how much the hole in the shank would expand. I think having a reamer of the correct size to make a proper shrink fit defeats my objective of devising a simple way to make a rigid, self starting extended drill with the tools I have on hand.

However, I agree with your suggestion to buy an extended length spotting drill. (Of course I still will need a taper length drill bit to finish the hole.) Where do I buy the extended spotter? Did not find anything that meets that description at McMaster. Not for the size holes I am drilling.

 

[Engineeringtech]

Swifty - I'm going to experiment with some Loctite stud and bearing lock. That might hold up to the heat of drilling.

Goldstar31 - I'd love to be able to slver solder the drillbit to the shank without warping it, or losing the hardness of the cutting edge, but I'm not very good with a torch. Maybe it is my silver solder and flux. Can you suggest something that works well for this application, and where I can buy it?

 

[Swifty]

Norman, I have a dread of D bits, I fully understand that they can be very effective in certain instances. My dread started when I was an apprentice, there were a several German toolmakers employed and I was under their instruction. They used D bits to ream holes in diesets to locate dies, the hardened die acted as a guide. I was using a HSS D bit to ream a hole, but the D bit ended up seizing in the hardened die and shattered. That was it for me, always used reamers after that.

Paul.

 

[Swifty]

Swifty - I'm going to experiment with some Loctite stud and bearing lock. That might hold up to the heat of drilling

Even if the drillbit warms up a bit, it should not affect the loctite, you can always use coolant to stop any heat buildup.

Paul.

 

[Engineeringtech]

Paul,
.........Is a casting actually flat? No it is not. If ANY drill is presented, it will wander on the uneven surface and probably the surface is chilled. Back to the drawing board! So we have get a flat surface( it gets worse on a bit of round) but you need an end mill. ....
So you now have a flat surface. You can centre punch it, whatever you are going to follow up with a centre drill to open up a way for the size drill. .......
Norman

Norman,
Thanks for your suggestions. Actually however, In this case, the bottom of the casting is quite flat and smooth. (The sides of the casting are not. On those I used an endmill to flatten the surface before drilling.)

I have been known to use Onsrud single flute router bits to plunge right through the side of a casting. They are rigid enough to do this, and don't wander like a drillbit. However, you have to worry about chatter, and they are only available in limited sizes, so I usually have to follow up with a standard drillbit.

 

[Engineeringtech]

Norman, I have a dread of D bits, I fully understand that they can be very effective in certain instances. My dread started when I was an apprentice, there were a several German toolmakers employed and I was under their instruction. They used D bits to ream holes in diesets to locate dies, the hardened die acted as a guide. I was using a HSS D bit to ream a hole, but the D bit ended up seizing in the hardened die and shattered. That was it for me, always used reamers after that.

Paul.

Swifty, I liked your idea about Loctiting the bit into the shank. I think a stud and bearing product will be more resistant to the heat than standard loctite. I just haven't had the chance to try it yet.

Norman, would you explain how you make a "D" bit? I assume you are talking about a piece of drill rod turned to the diameter of the intended hole, hardened and a flat ground on one side? I have tried things like that before, but they certainly aren't self starting and the ones I made don't seem to clear the chips well. It seems to me they need some relief behind the cutting edge, but how do you hand grind this without risking botching up the cutting diameter?

 

[goldstar31]

We've been at this silver solder thing rather too long. There are lots of really unnecessary comments about what is really a simple operation. If my missus could bend and then solder stainless steel wire at 18 and then my daughter likewise, then 'why is all the fuss being generated ?'

If you can go out and buy a simple borax flux and a length of high silver solder, there is nothing to it. My wife did her thing with a mouth blown methylated spirits or alcohol burner- so sorry- but there are plenty of books. I tend to use Bill Bennett's edited George Thomas's Model Engineers Workshop Manual. Bill and my missus were dental students together - not engineers. I'm not an engineer either. On my bookshelf is one set of instructions on how to do it by Ian Bradley in his Drilling Machine book( MAP books) whilst my very moth eaten LBSC book on building Maisie in the MAP series has how to do it- and a boiler for the loco with a coke and kerosene thing- that would terrify me now. I have no doubt that the British Tubal Cain added his version but I donated most of my books to a younger generation years ago.
I'm a City and Guilds bloke- or was, and it was right to pass on -what had served me well!

As for D Bits, I would get into the Ian Bradley books as mentioned. It doesn't need soldering methods and more or less halving a rod and putting a sharp edge isn't too difficult. I recall squashing my thumb and the works nurse drilling with a D Bit made a hole in the nail to let the blood out. the D bit was a darning needle stuck in a bit of cork or pencil. I was brought up in the high hills of Northumberland/Durham border. Bagpipes were drilled with the shepherd's wife's steel knitting needles- sharpened on the sandstone window sills in a kerosene lit cottage. It isn't difficult.

I was a kid and made model aircraft to scale using broken glass from greenhouses that had been blown in in the Blitz. My drill came from Woolworths for six pennies and I used a safety razor blade that was finally too blunt to do Dad's stubble.

Simply persevere. You might get to be a grumpy old Know it all of 84( next month) but you will learn and learn- and still learn.

Tempering is- well, stick it , red hot in a potato. Old age- I'm forgetting- sorry.

Norman

 

[MachineTom]

A spotting drill is used to start a hole it "spots" with a very narrow drill point. The diameter is should be larger than the hole you want to drill. A 1/4 x 4 " drill is $29 from MSC, then drill with the #26 6" drill.

Do not try to drill through with a spotting drill, there is no edge relief so it burns.Just make a spot that is eyeball bigger than the proper hole.