Thick stubby drills

[PekkaNF]

I seem to be running out of daylight increasingly often.

Stubby drills solve problem easily until 8-10 mm diameter, but larger, specially 16-25 and over is a problem.

1. Mount: MT3 shank is long, straight shank would be nice, specially 16 mm dia. How is the Rotabroach type?

2. Drill length, are there drills that would have close to same lenght, short shanks over 12 -> 20 mm (or close) diameter?

Thank you,
Pekka

[PK]

Stubby ball nosed end mills?
I seem to have a collection of large drills that have either been cut short with an angle grinder and re sharpened, or extended with a welded on shank. 
You just can't win I guess...

IIRC rotabroach cutters mount on an arbor. So making an MT3 or parallel shank adapter shouldn't be hard???

[12345678910]

Are you familiar with

Silver and Deming Drill Bits



http://www.norsemandrill.com/pdf/prd/type130-AGM112014.pdf

If you can find a real industrial supplier with a paper catalogue in your area; you can learn a lot by flipping through the photos
 

[chipenter]

I got rotabroach cutters mounted in a collet to give me more daylight , but they are smooth cutting and will cut large holes in one go , run slow as they are difficult to sharpen the offset teeth corectly .

[PekkaNF]

I have one 16 mm ball nose slot drill and I have used for drilling, plunges better than straight slot drill. I have about 1,5t knee mill w/o pinole = feed is by cranking the knee. Speed 25-700 rpm about 3,5kW, 22 mm slottdrill will go trough hot rolled metal, but shakes the table.

I have been thinking of sharpening some chipped slot drills to "drills", but I don't have them in sizes I want. Positive thing is that ER25 chuck is pretty compact and MT3/16 mm collet is even more compact. IF there were some short drills with 16 mm straight shanks in 12-20 mm sizes it would solve many of my needs.

I don't like "Blacksmith Drills" most of them are pretty poor quality, I have some, but it seems to work better to start with a standards drill and turn down shank.

Googled some Rotabroach and there seems to be MT3 taper adaptors for them, with coolant union and all. Downside is that they get pretty long fast. But Rotabroach shank looks a little like weldon shank, but it is OD19,5mm, has two flats at 90 degree where set screws butts.


This sort of set looks fine:
http://www.toolstop.co.uk/unibor-magnetic-drill-cutters-set-of-6-p72509

* Sizes 14S, 16S, 18S, 20S, 22S, 24S, pretty much most I will need
* One lengt/shank for all
* But I should turn own adapter from MT3 taper blank (not too hard), but if it needs trough coolant, it gets a bit more complicated.

Chipenter: What collet system you used? Did you use use 12-30 mm Rotabroaches? What rpm and how much coolant you need? I have no problem with low rpm or high feed, but coolant might be a issue.

Maybe I buy one locally (If I can find one after my work day) and make one adapter as a weekend project just to find out how it works out?

Pekka

[Spurry]

I use the Rotabroaches in an adapter made to fit the 20mm R8 collet. The short ones are good for about 25mm deep cuts, but need frequent clearing. My adapter adds about 75mm from the collet nose to the broach cutting faces.
Pete

[PekkaNF]

Thank you, I think that rotabroach is way to go. I went to buy one 20 mm dia short rotabroach....they had none. Bummer.

Looksl like the rotabroach is the solution.

Pekka

[chipenter]

I use mt3 collet without slipages so far, the largest rotabroach I have is 35mm tct tiped runs between 80 to 120 rpm , depending on the hardness know power coolant just a spray bottle , mag drills run slow a search on the speed should help there .

[PekkaNF]

Thank you.

Are generic brands mostly marginal? Are there better brands or should I get two real rotabroatches (mostly need 20 and 24 mm) or buy something like this:
http://www.toolstop.co.uk/unibor-magnetic-drill-cutters-set-of-6-p72509

Pekka

[chipenter]

Now idea on brands most of mine are second hand , it's the grade of material you pay for HSS Cobat or TCT as with all cutting tools you get what you pay for .

[PekkaNF]

OK, got a set of most likely sizes. Rotabroach brand. It's going to take week before I'll get them, bit time to figure out how to mount them.

Pekka

[PekkaNF]

Haven't got the Rotabroach cutters yet, thinking of minimum cage length MT3 to Weldon adapter.

I'm considering making a simple MT3 to 3/4" adapter, minimum length. Nothing complicated there. However rotating coolant inducer would be interesting and probably even useful.

Has anybody here build coolant inducers, something like this:
http://www.rotabroach.co.uk/wp-content/uploads/2015/06/Morse-taper-arbor-up-view.jpg

Can't really see how I could build it super short, without going into very thin metal and here I will be using few hundred rpm and there is three times more power than magnetig drill has (Although I hope I don't need all that).

MT3 business end is about 24 mm dia and there needs to be enought meat for 19,05 mm (3/4") weldon. This Weldon seems to be of 23 mm lengt, two flats 90 degrees appart.

Lenght: Need some 6 mm for dog (27mm dia, 24mm  flat, max od 38mm) and looks like very little extra lengt would be needed if I could squese the coolant inducer into 15 mm long space, diameter can be large.

Would Plastic (nylon) or something do, clamped between two metal washers?

Just toying with this coolant inducer, I haven't build any yet, but this is easiest application and I have tools that really could benefit from trough coolant capability (those are bit more pressure though).

Pekka

[awemawson]

Over engineering it. Just use a squirty bottle of coolant 

[PekkaNF]

Yup..could use bottle, but I'm not any more ambidextrous than bilingual....and automatic coolant feed is easier than drill feed.

Anyway I though that if it is not too bad and does not really add much length (and take much time), I could learn something here.

I might go for it (or not) or build it to work without the rotary parts even if it fails.

Pekka

[PekkaNF]

Should get the Rotabroaches tomorow. Bearings, bits and seals should drop into mail box this week.

I haven't found many details/cutouts of the coolant inducer. My gut feeling tells that in this application simple POM/Nylon bushing shoudl work:
* I'm planning to use simple gravity feed little above of the mill head = pressure is low, volume is low
* low rpm
* a little lead does not hurt
* Takes up little axial play
* Some front feed drills seem to be fine with it!

But I started thinkkin...I have drills that have coolant channels and they could use whole lot higher collant pressure:

1) Normal shaft lip seals are fine to about 0,7 bar, there are high pressure versions, but they are not common stuff in bearing shops
http://fpparis.com/en/products/high-pressure-oil-seals

2) Whattabaut...PTFE/POM disc backed up with a DIN 988 ring?
http://www.cutwel.co.uk/filedepository/product-images/hole-making/indexable-drilling-systems/supercut-spade-drill-system/coolantringbp-1.jpg

3) I like this construction, but what material and purpose each seal part has?
The picture athe end of the page is interesting.
https://us.bigkaiser.com/products/coolant-inducers/hi-jet-holders.html

4) I googled hydraulic rotary seals and looks like whole lot of them are made with orings or with a backup ring and oring....then found a construction that seems to have a seal ring against rotating shaft and a oring as a elastomer to put pressure to this ring and to to seal he cavity.
Picture here clicks bigger:
https://en.wikipedia.org/wiki/Rotary_union

Pekka

[PekkaNF]

Finally I got my parcel....PostNord sat almost week atop of it. Express my hiney.

Anyway I got real brand name Rotabroaches, set of short 14-20 mm dia and extra 25mm OD. Rushed to make an MT3 minimum lengt adapter and plan was good, but the MT3 blanks that have been joy to work before turned me down. This one was made of mysterymetal and it was proverbial to work with.

It had a nice 40 mm ground outside, checked it and it was true, drilled and bored the 3/4 hole, with some difficulty, beacause the material was "sticky", got a little oversize hole (19,06 mm). Then I turned the oil grove (planned to place an angled hole from it to rear of the cutter recess. All well and original ground surface was saved for the cutting oil seal (Grub screws were M12*12 and could be shortened just a bit to clear Nylon or acetate bushing that plays the role of the seal....or that what I had in my dreams.

Went nearly acceptable, but when I threaded the M12, it raised the metal around the thread. Had to turn down the perimeter and now it is not anymore good enough finish for any kind of seal. Bugger.

Had no time to test. Hope it works. I would have liked the blank a tad longer (it is 30 mm long, dog ate 7 mm of it at the tail and web left behind of the weldon seat is thin. But that was only thick enough blank I had.

Well, I call it POC.

Pekka

[PekkaNF]

Got parcel from Germany, same size/weight parcell ordered a little later 1/3 price of P&P and 1/20 of aggravation...looks like I'll be ordering more stuff from EU than from Brexit.

Anyways I declare this partial success. I was planning to use this one to check coolant feed troughh nylon bushing, but the MT3 blank does not finish easily to any kind sealing fit without resorting to grinder and that creates it's own set of problems....mainly the fact that I haven't used mine yet.

Got 30 mm ID 42 OD ball bearing and same size shaft seals, planning to make other adaptor for trough coolant feed.

Questions:
* How to produce good enough finish on shaft for lip seals on HMS? I have grinder, but never used it for a real work - to achieve certain shaft roughness. What kind of grinding stone for normal hot rolled bar stock, drawn bright stock and tempering steel?
* How to grind it dry? I'll still need to order curtain and cobble up an shop vack adapter, because the cast iron fan I had was way too heavy.

If it turns out to be too hard, I'll probably put this project aside until I have the grinder all sorted out, might as well do the whole adaptor from bar stock MT and all.

Pekka

[PekkaNF]

Just a little progress. Have to add reaction bar to hold the inducer. I don't want it to do flail imitations.

Not sure how well it will hold the coolat, but that piece was an off cut and it't the first try. No lipseals or such.

With third (coolant) hole it starts to look bit like a swiss cheese.

Pekka

[sparky961]

* How to produce good enough finish on shaft for lip seals on HMS? I have grinder, but never used it for a real work - to achieve certain shaft roughness. What kind of grinding stone for normal hot rolled bar stock, drawn bright stock and tempering steel?
* How to grind it dry? I'll still need to order curtain and cobble up an shop vack adapter, because the cast iron fan I had was way too heavy.

Pekka

Did you get the finish sorted out?  I'm assuming by "HMS" you mean hot rolled mild steel.  I find this easier to turn than CRS (cold rolled steel) but can still be tough to get a nice finish.  In "my" CNC lathe at work, the solution is to CUT HARDER and CUT FASTER... seriously.  If the chips aren't pinging off the inside of the enclosure and you can't hear the motor working, it isn't taking a big enough chip.  Really nice surfaces this way too. 

Unfortunately few on this forum have machines like this at home to work with (myself included), so the rest of the mere mortals need to resort to emery cloth, sandpaper, files, steel wool, and such.  Sometimes, if you're really lucky, you can get an insanely sharp piece of HSS to do the trick.  Put the carbide away unless you're going to be hogging away material.

Try to see what your machine is capable of.  Set aside some of your tooling budget to break a few things while testing.  Wear a full face shield and have the e-stop readily accessible.  HOLD PARTS FIRMLY.  Feed seems to give more favourable results than depth of cut, but you don't want to be just scratching off a few thousandths either.  I suspect it's some sort of burnishing effect going on.

[PekkaNF]

I used file + emery... not proud. It is nowhere any known even metric (or probably even fractional inch) dimenssion, just tried to keep the errors on right way...

I actually get pretty good finish on tempering steel when using sharp carbide tools and a lot of cutting speed, swarf must be hotter that violet. DOC is minimum recommended and feed just short of stalling the lathe. Then piece is true and finish is good.

Problem is that you have to sneak to diameter, because all finishing cuts must be about the same depth. I'll put TDI to cross slide, mike diameter and try to fine adjust the cutting depth (e.g. recommended minumum is 0,3 mm DOC, I'll play something like 0,3 - 0,5 mm) to hit final diameter in three or four successive cuts, trying to keep the DOC as constant as possible, but may need to adjust each cut to make last cut same DOC as previous. Some can count on cross slide dial, mine is not that great somewhat between metric and imperial....close to both, but not close enough.

I never had predictable results with hobby type finishing "shaving" cuts for last few "thou". Although I have learned a lot of sharpening HSS and I see the benefit. maybe it works on free cutting steel?

I may need to learn my own MT3 tooling, including tapers and testing equipment.

Pekka

[sparky961]

See if you can find some 4140HT or 4340HT. Its a bit tough to break the chip at lower feed/DOC but getting a nice finish is relatively easy. You also end up with a part thats moderately hard but not brittle. This is my go-to material for one-off thread gauges and other tooling.

[PekkaNF]

As luck would have it, I have 42CrMo4. Tempered form.

36CrNiMo4 is whole lot harder to work with, specially internal threading or long holes. Makes very nice shaft though.

Pekka