Hole Saws

[bp]

I'm about to start construction of a QCTP for my C3 Mini Lathe.  Its going to have the "Toolblock Clamped to a Central Pillar" style of construction.  This obviously requires the generating of a pillar size hole in the individual tool blocks, currently I'm looking at a 32 or 35mm diameter pillar to maximise stiffness.  Either in the lathe or on the X2 mini mill, this equates to a lot of swarf.  I obtained a quote for water cutting the holes, $432 for twelve holes which struck me as being rather excessive, obviously they aren't interested in small jobs!!  Then I thought of a hole saw, which seem to be fairly readily available and are advertised as being ok for steel, a bonus might be the production of lots of little billets of steel from the centre of the hole..........
Has anyone used hole saws for this purpose?  Are they any good, how do they last etc etc 
Anyone have any comments suggestions.
Cheers
Bill Pudney
Adelaide, Australia

[Jasonb]

I've used them on steel plate and CI pipe but only upto about 6mm thick. For what you are talking about you will get through a lot of holesaws and it will take a long time.

Don't know if the hollow cutters used in magnetic base drills would be any better would have the advantage of not leaving a pilot hole so the billets would be more useful.

Either way you will still ned to finish the bore with a boring head or bore in the lathe

Jason

[SKIPRAT]

Hi Bill
I have cut a hole 110mm diameter using a cobalt holesaw in 25mm thick boiler plate for a solid fuel stove flue pipe adapter ring on an backgeared industrial pillar drill.It was fairly slow going backgear engaged and spindle speed of 82 RPM plus the occasional squirt of coolant,the slug produced may well have further uses but it will have a pilot hole in it

Cheers Paul

[andyf]

Hi Bill,

The only time I've used a hole saw was with a 25mm HSS one to make holes through two pieces of 12mm ali alloy, for subsequent boring out to 30mm. I did it on the milling machine. For the first hole, I had to use very low speed (no more than 60 rpm, I think; my machine has a sort of back gear). Down feed was very slow; after all, the 25 or so teeth round the saw were each 1mm wide, so it's a bit like using a parting tool 25mm across. Chips accumulated in the narrow circular groove which slowly formed, and were progressively harder to remove as the groove got deeper.

Learning from all this, I put a 6mm pilot hole through the second piece, mounted it on a peg (very poor man's rotary table) and chain drilled 4mm holes around a 25mm circle before changing to the hole saw with its 6mm pilot drill. That went much quicker, because the saw only had to cut the 1mm or so webs between the holes, and the chips found their way down the holes.

I don't envy you the task of making a dozen toolholders each 25mm deep. I suppose they are along the lines of the Norman Patent one shown here http://www.aardvark.co.nz/pjet/qctp.shtml . You might consider a bit of a redesign along the lines shown here http://mikesworkshop.weebly.com/novel-quick-change-tool-post.html
and here http://mikesworkshop.weebly.com/improved-version.html 
so that you can do away with the clamp bolt and fit two tools into each holder, each with its own height-setting screw. That would mean you would only need six of the things.

Andy

[fatal-exception]

I've used holes saws in the past for alot of things, but like the other say, they are only meant for up to a certain thickness, especially in steel.

Here's the last thing I did with a hole saw. It took a few minutes per hole and the plate is 3/8" (10mm). I was pleasantly surprised at how well it went. The holes are 1 1/2" diameter since that's the hole saw I had on hand. It is made by Starrett, but the Bluemol and Rigid ones are just as good imo.

Why not bore the holes on your lathe?

[RichardShute]

I have used a hole saw of the HSS-Bimetal type (ie a 'good quality' one, not Chaiwanese el-cheapo carbon steel) to take out a core of cast iron in some chuck back plates. I did about 8 or 10 in a batch and it was worth the saving in swarf, time and to have the centre lumps left over for other 'little' jobs. The hole saw is still good for plenty more work. I shortened the pilot drill and once the saw is in 1/8", you don't need it, the circular slot guides the saw OK. I went in the full depth of the saw from one side, then turned the blank over and did the same from the other side, just enough depth to meet in the middle. It was a 1-1/2" hole saw as I recall so about the same size as you are considering.

The two main issues are speed and clearing the swarf. I used the lathe as it will run way slower than the drill and is obviously far more rigid. Also, being horizontal, the swarf clears more easily. For steel, I'd probably use a lot of coolant and withdraw the saw very often to clear it. If you use the drill I would definitely recommend clamping the work down with a clamp, not just hand held in a drill vice.

Richard

[bp]

Thanks guys that's all pretty positive I'll try and get a good quality hole saw and report back!
Andy....I did look at the collet style but what concerned (concerns) me is the collet and its wedge.  I drew one with two wedges, top and bottom and a reduced angle, 15 degrees instead of 45.  It still has its appeal, but after some thought the plain pillar with a clamp on toolblock won out, for now and for me at least.  Also Andy I like your chain drilling idea, that's certain worth a shot

I thought of doing all of the operations in the lathe, certainly not hand held with a drill!

I'll have a search for a decent hole saw here in deepest darkest Adelaide
Cheers
Bill Pudney

[RichardShute]

As it happens, I ended up doing one this morning and it prompted me to remember a detail. In order to avoid the hole up the middle from the pilot drill, I machined a small spigot about 1/16" high to act as a pilot inside the hole saw. Also, for a casting, it gives a fair surface for the saw to start on, bare casting makes it wander all over the county even with a pilot drill.



and the core for later use.



Richard

[bp]

Well I got a 32mm HSS Bi metal hole saw.  Advertised as being "Australian made" but bearing "Made in USA" on it!!  It made it about 6mm into my 25mm thick blocks, at about 80rpm, and VERY SLOW feed on the mill.  So I gave up on that as it was not a smooth process, the whole time I was waiting for something to go bang...which it didn't fortunately.  So I tried the boring head in the mill.  That was almost ok, except that it produced a tapered hole, not due to tool spring or anything like that, at least I don't think so, still haven't worked out exactly what happened.  So I have now completed the second and third using the four jaw and boring them in the lathe, drilling to 12mm (my biggest drill) then boring with the biggest stiffest boring bar I have.  Its one of a Chronos set, although I've seen them elsewhere, pre-ground HSS.  It takes a while, but produces a nice clean smooth accurate bore, and produces a huge mountain of swarf!

I assembled one onto the lathe, and will use it tomorrow to bore the next few.  So far its seems a quantum leap better (stiffer) than the original QCTP supplied with the lathe.

I will try and get the Boss to take some photos....yes I know its only another bl**dy QCTP but someone might be interested, amused, encouraged, put off etc!!

cheers
Bill Pudney
Sunny Adelaide.

[Spurry]

I'm surprised there appears to be so little enthusiasm for Rotabroach cutters. After a recent discovery, I think they are the greatest thing since sliced bread.

I used a 12mm one for through-drilling some mild steel box section with excellent results. A 25mm one went through some steel channel good enough for an axle.

There are none-generic ones available but they don't seem to cut as well...in my limited experience. The pic shows 25mm holes in 1/2" plate with the U channel.

Pete

[bp]

Hi Pete,
I looked for Rotabroach cutters, and was a bit startled....well gobsmacked really....at their cost.  Don't forget that I'm in Australia and it costs several arms and legs to get "stuff" here, this tends to be reflected in retail costs.
I've now worked out how boring in a small lathe got its name!!
cheers
Bill Pudney

[Warrenm]

With the way the Aussie dollar is at the moment, it's well worth looking offshore.

[Ned Ludd]

Hi Bill,
If you want the ultimate tool for the job take a look at;
http://www.iscar.com/ProductLines/ProductLineDetail.asp/CountryID/1/ProductLineDetailID/3
Well I don't know about you but one can at least dream.
Ned

[Jonny]

I have to do those size holes and bigger on daily basis but mostly in aluminium which has numerous disadvantages.

If you can get the job in a 4 jaw on lathe drill or open up as much as you can, my instance is a 28mm because largest available in MT3.
I then open up by boring out, heres a something simple 130mm o/d with 42.2mm bore.
http://pic20.picturetrail.com/VOL15/728921/1252422/311844089.jpg
Removing 1/2" facing off one pass http://pic20.picturetrail.com/VOL15/728921/1252422/14582043.jpg
Showing 42.2mm bore x 15 deep http://pic20.picturetrail.com/VOL15/728921/1252422/14584596.jpg
I can fill a wheelie bin with swarf within an hour next alum will be free cutting with small chips.

Hole saws are used to originally put the main 6 holes in http://pic20.picturetrail.com/VOL15/728921/1252422/14584660.jpg without centre drill.
Then bored out individually on rotary table, easy done well over 500 over the years.

In your case hole saws waste of time, drill and bore out which will take an eternity on such a small lathe.
Your boring bars will be flexing i have brand new unused from that place, totally worthless. No substitute for quality robust tooling ala Kennametal, Iscar Ceratizit, etc Could get away with the cheap brazed 1/2" round shank such as http://cgi.ebay.co.uk/RDG-CARBIDE-BORING-BAR-SET-1-2-12PC-SET-BORING-HEAD-/370142246041?pt=UK_Home_Garden_PowerTools_SM&hash=item562e327499  May take a couple of hours per hole though but no alternative.

[bp]

I've now done 6 toolholders.  The operations so far have been
1/  in 4j, face both sides of 25mm slice of 50mm x 50mm S1214, approx 10 mins per block  (all12+2 parting toolholders complete)
2/  mill 10mm deep x 11mm high tool slot in one face, various methods ( hog with a 3/8" end mill, very slow;  slitting saw top and bottom faces, end mill the rest, painful; the best was a good quality (Dixie) end mill) the best is about 25 minutes per block (all 12+2 toolholders complete)
3/  drill and tap 2 x M6 x 1 x 30mm deep full thread, clamp screw holes, about 35 minutes per block (all12+2 toolholders complete)
4/  mark out all holes on top face..tool clamp screws (3 off), height adjuster (1 off), toolpost centre (1 off) 5 minutes per block (all12+2 toolholders complete)
5/  drill and tap 4 x M5 x 0.8 threads, for tool clamping and height adjuster holes, and centre drill toolpost centre, about 20 minutes (6 off toolholders complete)
6/  set up in 4j, 5 mins average, drill in 3 steps to 12mm dia, then bore to 34.5mm dia to fit pillar, about 1.5 hours per block(6 off toolholders complete)
7/  with slitting saw, cut clamping slot about 5 mins per block(6 off toolholders complete)
8/ deburr and clean about 15 mins(6 off toolholders complete)

Its just as well I'm patient!!
cheers
Bill Pudney

Its a fair amount of time involved, but I'll get there!!

[dsquire]

Jonny

Saw your post on turning and boring the aluminum discs. I am curious as to what they are used for. Are they part of a wheel for RC vehicles? What ever they are, it looks like a fine product. 

Cheers 

Don

[Jonny]

Its the tapping that would scare me BP, having broke an M5 tap in the job Friday trying to be clever.
Certainly have to make do with what we have.

Don they are focus wheels for optical instruments.
Bit of swarf created this week all for SA http://pic20.picturetrail.com/VOL15/728921/1243489/389520840.jpg

[bp]

"Its the tapping that would scare me"

No worries, just take it easy, back off often and away you go.  So far 2 off x M6 x 1, 30mm deep (blind hole), plus an M5 x 0.8 25mm deep (through hole) and 3 off M5 x 0.8 by 10mm deep per completed toolholder.

I tap ALL these holes the way (as far as I can remember!!) I was taught during my apprenticeship back in the '60's.  All holes were drilled and tapped in the mill so no X axis or Y axis movements are needed between drilling and tapping.

1  Drill to tapping drill size, using a decent drill, so the hole finish is ok.
2  Csk entry point for tap to about 0.5 mm over thread size
3  Using a good sharp HSS ground thread intermediate tap in the first instance, with a spring centre in the mill chuck to maintain alignment and some lubricant I use either a paste which I scored from work on aluminium, or "Rapid Tap" in steel.  The experiences I've had with buying cheap, carbon, taps has encouraged me to get good quality, HSS Ground thread.  Examine a carbon tap with a good loupe and ask yourself the question "how will those burrs affect the thread that I'm trying to generate".
4  Half a turn clockwise, quarter turn anti clockwise until you feel the chip broken off, both GENTLY, until the thread is established, when the clockwise bit is extended a bit.  Always holding the tap wrench carefully and being aware of whats going on.  If the force required suddenly rises for no reason ....STOP.... back out gently and clean the tap
Remember that the forwarding and backwarding (is there such a word??) is to generate a chip in the first place, then break it off in the second place.
5  Change intermediate tap for a plug tap, or bottoming or number 3 or whatever the last tap is called in your part of the World.  Lubricate and CAREFULY pick up thread, then wind last tap through still using the 1/2 turn forwards and 1/4 turn backwards routine and the sprung centre.

Bingo one nicely formed fred.

In all of the above the following are REALLY important I believe

1  Maintaining alignment between drilling and tapping.  If not in the Mill USE A TAPPING GUIDE
2  Avoid ANY side load on the tap
3  Use a good lube

Like a lot of things its technique rather than luck
cheers
Bill Pudney

[andyf]

All I would add to Bill's technique is that if the tap seems to jam up on a backwards turn, don't try and force it. Just go forwards again and cut a smidgeon more - a tenth of a turn or less. That usually frees the jam. 

Andy

[Jonny]

I would have no hesitation drilling and then substituting a tap doing it in one go with M8 and above in some steels.
Aluminiums wouldnt even use machine taps but do use them recently, they even work better hand tapping for some reason. Regularly drill through 3.3mm dia, substitute for 4.1 and drill half way, substitute for 8mm region drill and counterbore for csk screws then finally without moving off centre slap an M4 tap in and drop to very low revs- Next hole easy.
Only about 1" thick heres one i did earlier, well last year http://pic20.picturetrail.com/VOL15/728921/1243581/379943872.jpg