Needs Pictures: 0
Results 1 to 15 of 31
Thread: Off centre drilling--lathe
-
22nd Oct 2018, 03:49 PM #1Senior Member
- Join Date
- Jun 2011
- Location
- gold coast
- Posts
- 303
Off centre drilling--lathe
Hi Guys,
I feel a bit helpless at the moment when I cant track down a problem myself, but in act Im stumped.
I set up a simple turning job in aluminium on the weekend.
Drill a 5 mm hole through a 65 mm long piece of 20mm diameter stock.
Counter drill 50 mm deep to 13 mm ID.
Of course I took it in stages (8mm, 10mm, 12mm, 13mm)
When I took the part out of the chuck I noticed the 5mm hole was off centre at the 'other' end by almost 3 mm.
I set up a second piece of stock and drilled right through to 5 mm diameter again. Same outcome.
I used WD40 as a lubricant and drilled in small 5mm stages.
I set up two 200mm lengths of 6mm ground stock, one in the three jaw and one in the drill chuck in the tailstick so they almost touched.
I lay a straight edge along the top and there was no light gap so I assumed the centre lines are the same???
Maybe a bad assumption?/
So Im stumped.
I'm open and grateful for any suggestions please
warm regards
Brian
(PS Ive tried to upload a pic without success---sorry
-
22nd Oct 2018, 03:57 PM #2Senior Member
- Join Date
- Jun 2011
- Location
- gold coast
- Posts
- 303
Offset drilling lathe problem pic
Heres a pic I think
regards
Brian
-
22nd Oct 2018, 04:08 PM #3Most Valued Member
- Join Date
- Apr 2012
- Location
- Healesville
- Posts
- 2,129
3mm... sheeezz... is the chuck mounting clean and tight?
If so extend a length of stock say 100mm out of the chuck and put an indicator on it near the chuck and then at the end and see what you get
-
22nd Oct 2018, 04:13 PM #4Member: Blue and white apron brigade
- Join Date
- Feb 2006
- Location
- Perth
- Posts
- 7,189
What sort of tolerances are you talking about?
I assume you want a 5mm hole 15 mm long at one end and a 13 mm diam hole 50 mm log at the other?
First thing I would look at is the bit - is it and old 5mm bit? If so I'd try a new drill bit.
It's not what I would call precise but if you are not after high precision the way I would do it is with a 6mm (minimum) drill to a depth of 50 mm and then use a 13 mm bit - ie no staging. Then drill a 5 mm hole from the other end.
To drill long holes from one end with small diameter bits I usually start with a shortened bit so the first 6mm bit will be short - then I switch to a standard bit and then to a "long" bit.
I keep broken bits and repoint them so over the years have most of a set of so called "shorts" - "longs" you have to buy.
-
22nd Oct 2018, 04:21 PM #5Most Valued Member
- Join Date
- Jul 2016
- Location
- Melbourne
- Age
- 35
- Posts
- 1,522
I would definitely suspect the drills, I would probably start the hole with a very short stub length starter drill then I would drill the counterbore first all the way to 15mm then punch the smaller hole the rest of the way with the shortest 6mm I could use.
I definitely wouldn't use that many drill to open the counter bore up.
-
22nd Oct 2018, 06:16 PM #6Philomath in training
- Join Date
- Oct 2011
- Location
- Norwood-ish, Adelaide
- Age
- 59
- Posts
- 6,561
As others have said, you are stepping too much. A pilot drill only needs to be around 25% of the diameter of the finished drill - it's only purpose is to provide clearance for the web of the next size drill up. Now if your drills are not sharpened properly or have some damage on the tips, then one side will cut more than the other and that will tend to make the drill wander. Drills also follow an existing hole, so if one of your drills has wandered then the hole is doomed...
I have a small carbide boring bar (Kennametal I think) that takes a CCMT06(?) insert. That will start in a 9mm hole, so ideal for boring out a small part like that. I must admit that I rarely drill holes bigger than around 9 or 10mm on the lathe these days as the boring bar makes it really simple (and I need the practice)
Michael
-
22nd Oct 2018, 06:17 PM #7Golden Member
- Join Date
- Oct 2008
- Location
- Cairns, Q
- Posts
- 666
Cheat. Use oversize stock, drill it through then turn the O/D to size between centres.
Frank.
-
22nd Oct 2018, 08:05 PM #8Golden Member
- Join Date
- Oct 2001
- Location
- ACT
- Posts
- 667
a well sharpened drill and clearing the drill of swarf frequently can make a big difference also.
-
22nd Oct 2018, 08:20 PM #9Most Valued Member
- Join Date
- Apr 2012
- Location
- Healesville
- Posts
- 2,129
Adjusting your hole size
Just a quick bit of info, to drill an oversized hole in the lathe.
Just say for instance you need a 5.2 mm hole but you don't have an incremental drill that size, no reamer either, what do you do??
You sharpen the drill with a slightly longer cutting edge, and naturally the other side is a bit shorter and the tip of the drill is slightly offset, centre drill for your hole first.
Yep...you get a bigger hole and the hole that it drills is still pretty close to the centreline of the spindle.
or you can blunt one of the the cutting edges for the same purpose, drill pilot hole first.
So what I am getting at here is that even a bent drill should drill a straight hole in a lathe if it has a centre hole to start it first.
Just sayin"..... 3 mm is a hell of a lot to be out over 65mm ?
cheers, shed
-
22nd Oct 2018, 08:29 PM #10Most Valued Member
- Join Date
- May 2011
- Location
- Murray Bridge S Aust.
- Age
- 71
- Posts
- 5,959
Have you had this problem before? If so, the chuck may not be aligned sideways.
Is your lathe a flat bed, a slight bit of play sideways may be enough to throw it out, I have that trouble with my wood lathe.
KrynTo grow old is mandatory, growing up is optional.
-
22nd Oct 2018, 10:14 PM #11Senior Member
- Join Date
- Dec 2010
- Location
- Syd
- Posts
- 492
I know lots of people get lazy, start with a centre drill?
2 and 1mm steps seem excessive, short of lathe having no balls....or slipping tailstock.
-
23rd Oct 2018, 03:20 AM #12Most Valued Member
- Join Date
- Nov 2007
- Location
- melbourne australia
- Posts
- 3,228
When drilling deep holes I drill from both ends where possible. Even if the holes don't line up in the middle, the subsequent drill bit tends to align the two holes. I always start with a centre drill as mentioned above.
Chris
-
23rd Oct 2018, 04:23 AM #13Most Valued Member
- Join Date
- Nov 2007
- Location
- melbourne australia
- Posts
- 3,228
Further,
On my reading of the OP, it’s the initial 5mm hole that is wandering, so it’s not the stepping of the drills to get to 13mm that is causing the problem.Chris
-
23rd Oct 2018, 05:58 AM #14
Hi Guys,
When drilling small deep holes, it is vital that both edges of the drill cut exactly the same, otherwise you will get the effect that you have experienced.
Years ago I had drills specially made for me by Dormer so that I could drill a 5/32" diameter 6" inch long hole in full hard aluminium bar, and it had to exit within a few thou of spec ! A very difficult task indeed.Best Regards:
Baron J.
-
23rd Oct 2018, 09:24 AM #15Most Valued Member
- Join Date
- Jun 2011
- Location
- Australia east coast
- Age
- 71
- Posts
- 2,713
This is why gun drills were invented.
I've never ever had a hole wander off centre that badly and I've shoved some awful dodgy hand-sharpened bits into all sorts of material in a lathe chuck.
Normally I centre drill, pilot drill and then use the biggest drill I can to finish the job. Step drilling is a PITA and wastes time.
PDW
Similar Threads
-
Crotch Centre for Hercus Lathe
By Abratool in forum METALWORK GENERALReplies: 3Last Post: 31st Aug 2012, 08:02 AM -
Lathe Drilling Jig
By jack620 in forum METALWORK GENERALReplies: 14Last Post: 2nd Jan 2012, 12:13 AM -
thinking of buying a centre lathe
By tpjamcc in forum METALWORK GENERALReplies: 2Last Post: 27th Apr 2011, 12:45 AM -
thinking of buying a centre lathe
By tpjamcc in forum METALWORK GENERALReplies: 1Last Post: 27th Apr 2011, 12:14 AM -
Lathe basics: Spindle centre error
By Bryan in forum METALWORK GENERALReplies: 35Last Post: 3rd Aug 2010, 10:38 PM