Thread: Another Arbor To Turn - Suggestions Welcome.

Originally Posted by Retromilling

I guess it depends on how much spindle bore diameter you have ......

Certainly not a he-mannish No 5 Retro. My little Hercus is bored No 3.

Bob.

Well then machine the NT30 and M12 thread external part first . Then machine an Nt 30 internal taper in a blank held in a chuck . Use a piece of M12 continuous thread as a draw bar to hold it in the socket tight and machine the internal part .

Michael G was interested in finding out how I fared with my latest attempt at arborism so .....

I thought I had taken the easy way by purchasing a CTC arbor originally intended as a boring head mount. In hindsight I might have been better off modifying an ER25 / 30 taper chuck because they are partially bored out. The boring head arbor is solid except for the draw bar bore. CTC don't always supply what they have illustrated on their website. The arbor I received did not have the standard 8mm thick flange , the "flange " was about 20mm thick.

I think CTC use 1060 and harden it. Too hard for HSS. The cutting edge of the steel in my DTH and a couple of boring bars disappeared. Kennametal's KC5010 performed well at 900 rpm with a .080" depth of cut and a real dainty feed ( I had no desire to rip the arbor from the chuck by being greedy with the feed). Surprisingly, the finish in the second photo was the result of a .003"DOC. Interesting steel. Of course, I snapped a couple of corners off due to the interrupted cut.

Then it all got tricky. The steel is too hard to drill with HSS so I ended up using a masonry bit. The carbide tip is wider than the flutes of the drill. OK in a brick but not too good in steel. There's nothing to guide the drill so it wanders. And makes a bloody racket.

I had to find out if I could cut an M16 thread so I bored the sacrificial projecting part of the arbor 14mm in diameter and had a go. I can tap a thread.

Then I installed the arbor in the mill's spindle for a bit of accurate boring. I have to bore a hole 14mm in diameter about 60mm deep. It seems as if the steel hardness varies. I was able to make some headway with a cheap Chinese boring bar but it required continual grinding of the bar's brazed on carbide tip. It chipped readily. The waif like bar is an American solid carbide Micro 100. Worked beautifully but suffered from chatter when held by only 10mm of its shank in a collet. Because of deflection of the cutter due to the lack of rigidity, the hole is tapered.

I think I will have to buy a small diameter indexable carbide boring bar to finish the boring off.

Still, cheaper than buying an arbor from Kaiser.

BT

ps. I probably would have bowled a 1045 version over in the time I've spent on this thing.

I have a couple of small diameter Kennametal bars that may come in handy for this sort of thing -
One is 110mm long (min 10mm hole) the other is 125mm long (min 12mm hole). Any of use to borrow?
(on edit - I also have a Gurhing 14mm drill bit HSSCo complete with integral coolant holes - you could try that too.)
Looking at the drawing, you need to be 70 deep for that hole so with a small bar you will get chatter anyway. Can you cut the cone first so that you can sleeve the boring bar in something more substantial?

Michael

(I wondered what this STP fitting that Bob had was - rather pedestrian really. It stands for Steilkonus - Piccolo (Steilkonus is German for Steep Cone, Piccolo is the project name for the kaiser boring heads that we have))

Answer for Stuart (below). The STP fitting has a m16 thread on top then the cone. (So the M16 is at the end of the cone 50mm in)The hole Bob is trying to do is the 14mm tapping drill hole size. While the chattery bit probably would not disturb the tapping, the off line bit would.

Hi Bob,
Why so much over hang? bottoming the Y?
Couldnt you just make a bar for the biggest collet you have to hold your boring bar?

Or does it need to be that deep and I have my scaling out?

Stuart

I won't be mean and say what i could-but i did worry about how hard the arbor would be.

Can you do as Michael says and cut the taper with a larger bar and then either sleeve a small bar or use a carbide drill? A 14mm one will not be cheap though.

Another thought, can you bore the 14mm from the other side? After cutting the taper put it in the 4 jaw the other way and cut from L to R with a tool ground to suit? Or anneal the damn thing and hope the 30 taper doesn't move...

Ew

Can't go from the other side as a 30 taper only has 1/2" / M12 drawbar thread.

Michael

It would need to be a small bar but with a lot less overhang than from the other side. Hence the need to cut from L to R. Just another idea, but not really a very good one.....And it occurs that measuring the 14mm would be nearly impossible without removing the arbor from the chuck

I'll go back to my red wine and bookwork now.....

Ew

Originally Posted by Ueee

I won't be mean and say what i could-but i did worry about how hard the arbor would be.

Can you do as Michael says and cut the taper with a larger bar and then either sleeve a small bar or use a carbide drill? A 14mm one will not be cheap though.

Another thought, can you bore the 14mm from the other side? After cutting the taper put it in the 4 jaw the other way and cut from L to R with a tool ground to suit? Or anneal the damn thing and hope the 30 taper doesn't move...

Ew

Along the lines of what the .... did you expect !!!! hey Ew

Ha! I was lured by my previous experience where I bored the guts out of a CTC arbor to accommodate the Taster's 20mm straight shank. Because it was an ER chuck I was able to use my 16mm indexable bar, there was room for it and it wasn't too difficult.

My plan was to bore a 17mm hole to a depth of about 30mm and make a guide bush to fit the hole and to fit the M16 tap's shank, a hopeful aid to concentricity. Boring the taper would mess those plans up.

Somehow Michael the Miracle Worker managed to extract a drawing of the STP arbor from Kaiser. My debt to Michael deepens.

BT

After boring that Annway endmill holder out i would not do anything like it again in a hurry, even though i used my 16mm WMNG bar!

Ew

Originally Posted by Anorak Bob

I think I will have to buy a small diameter indexable carbide boring bar to finish the boring off.

Might be a good time to order those cermet inserts too bob. They'll have no trouble with this stuff.

Originally Posted by andrew_mx83

Might be a good time to order those cermet inserts too bob. They'll have no trouble with this stuff.

I was looking at the 10mm diameter version of this bar from CTC. STUPR INDEXABLE BORING BAR #I41

The triangular inserts appeal to me because of the three readily usable corners. The romboid CCGT inserts I use have necessitated the acquisition of yet another toolholder to make use of all the broken insert's unused corners. I'll have a search for cermet in a 11020... size.

I might get lucky Andrew.

Bob
Nice work, I admire your patience & perseverance.
Bruce

Originally Posted by Abratool

Bob
Nice work, I admire your patience & perseverance.
Bruce

I might be walking away from that nice work Bruce. I bought one of Sutton's whizzo cobalt 12mm bits this morning only to destroy the corners of the thing when I tried to open up the bore a whisker. For some reason the arbor is extra hard at the narrow end of the taper. I don't relish the idea of ruining my 16mm Goliath tap set trying to tap the stuff. 4140 is like play dough in comparison.

Ewan's apprehension was well founded. Still, I had to try.

Bob.