Drilling deep holes – 10x drill diameter – Runout?

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Drilling deep holes – 10x drill diameter – Runout?

This topic has 29 replies, 21 voices, and was last updated 7 February 2022 at 13:06 by Buffer.

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30 October 2011 at 18:07 #15542
Steve Withnell
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@stevewithnell34426
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30 October 2011 at 18:07 #77072
Steve Withnell
Participant
@stevewithnell34426
I need to drill an accurate hole in HE30 finished out with a 7/32 reamer. As a test run I set a piece of HE30 bar to truth in the four jaw, drilled a 3mm pilot hole with a new long series drill, keeping each “peck” less than the diameter of the drill. I brushed paraffin with a toothbrush to keep the flutes clean at each peck. Once I had a through hole, I repeated the drilling process with a 5.5mm drill and finished off with a new 7/32 reamer. I was running the lathe a little over 2000rpm for the drilling and very slow for reaming.

The hole in the practice piece is 75mm deep.

Then I removed the test piece from the chuck and re-set it so the exit wound was facing the tail stock. Having set the workpiece to truth on the OD, I then used the DTI to measure the runout, by running the DTI in the ID. – slightly less than 0.2mm TIR.

I checked the tailstock aligment and as best as I can measure, it’s better than 0.05mm over the distance (ie not perpendicular off-axis distance at the tailstock).

It struck me that I don’t know if 0.2mm is good, bad or indifferent for a properly set up chinese lathe! Any thoughts welcome.

If the DTI is reporting 0.2mm TIR, does that mean the drill only wandered 0.1mm?

What can I do to halve the error?

Regards Steve
30 October 2011 at 18:27 #77073
Ramon Wilson
Participant
@ramonwilson3
Hi Steve,

To me you are approaching the job correctly but the hole will only run as true as that first pilot hole – any subsequent drill and the reamer having a tendency to ‘follow’ the previous hole. As your first hole is quite small despite your care in pecking it’s this that is probably deviating rather than any error in your set up.

Are you drilling that first hole with a normal drill before changing to the long series?

If you are able to accurately turn the job round you may be better off drilling the initial hole from both ends, it’s surprising how accurate that can be providing the holding is true.

Failing that I would try using a larger drill for the initial hole and if possible before opening to the reaming size run a long series end mill if you have one (or a D bit) down as deep as you can to true the hole to give you the best chance of guiding the reaming drill.

Hope that gives you something to work upon to improve the 0.1 deviation

Regards for now – Ramon
30 October 2011 at 19:09 #77078
Clive Hartland
Participant
@clivehartland94829
My first thought is that your rpm at 2000 is very high! I would have done mine at about 400 rpm.

The 3mm drill even if slightly uneven lip length will wander even though you are pecking.

Alu being easy to cut will allow the drill to wander much easier than steel.

As Ramon mentioned, if you can drill from both ends and see what happens.

75mm is long for a 3mm drill and a more rigid type of tool may be better, perhaps again as suggested a ‘D’ bit drill.

I would think the weakest part of a helix drill is where the flutes end and the parallel shank starts, it wobbles from there.

I would also start with a stub drill up close to make sure of a good start.

Clive
30 October 2011 at 19:39 #77079
Ramon Wilson
Participant
@ramonwilson3
Err – 400rpm Clive? Hate to disagree but that seems rather slow to me, particularly in aluminium.

Taking it at a cutting speed of 500 fpm gives roughly 17000rpm – for the 3mm drill, so Steve is actually well too slow but taking it too slow will probably lead to crowding of the drill and even more deviation. A conservative 250 fpm gives appx 8500rpm so 2000 is still well short of the accepted surface cutting speed. Obviously very few of us have kit that will do these kind of speedsso a compromise has to be made but I do think there’s a greater likelyhood of deviation by going too slow.

The 5.5 drill seems very close to the reaming size too leaving only a couple of thou for reaming – I would have though 5.3 more the likely candidate running around a 1000 rpm.

My money’s still on an initial 4 – 4.5 drilling then the reaming drill.

Regards – Ramon

Edited By Ramon Wilson on 30/10/2011 19:43:15
30 October 2011 at 20:15 #77084
Clive Hartland
Participant
@clivehartland94829
I was going by what speeds I have on the lathe Ramon, I think my highest is only 820rpm.

I just find that at anything faster than 400rpm the WD40 smokes and it starts to run dry!

Clive
30 October 2011 at 20:38 #77085
Sub Mandrel
Participant
@submandrel
Do you have a means of rotating the drill in the tailstock? If both work and drill rotate in opposite directions at about the same speed. any errors cancel out completely.

Neil
30 October 2011 at 20:39 #77086
Anonymous
Right, flameproof overalls on; here are my thoughts!

If runout of the hole is critical I wouldn’t use the lathe. I’d drill the hole in the vertical mill and then machine the rest of the part using said hole as the reference for set up. The problem with using the lathe is that it relies on the drill being perfectly aligned axially and dead parallel to the rotation axis of the headstock. The one thing you can gaurantee is that it won’t be.

I agree with Ramon that the 5.5mm drill is too large, the reamer will be rubbing or not even cutting. I wouldn’t bother with a pilot size drill, just go straight through with 5.3mm. Larger drills will tend to follow any ‘wander’ of smaller drills so why not start with the largest, and stiffest, drill. Less ‘pecking’ needed too. Also, keep the feedrate up, that minimises any errors due to slight asymmetries in the chip size.

I also think that 400rpm is a bit slow; I’d be up at about 2000rpm for drilling, and half the speed, twice the feed for reaming.

My sequence would be; start the hole with a carbide spot drill, drill through with 5.3mm, ream 7/32″.

Here’s a thought, you could consider a carbide drill; like for like carbide is much stiffer than HSS.

Regards,

Andrew
30 October 2011 at 20:39 #77087
Chris Trice
Participant
@christrice43267
Starting with a stub drill is a good bet and then proceeding with a split point four facet drill. I’ve found the latter tend to self centre better than a regular jobber drill. I don’t know why but they do, possibly because they require less pressure to cut. The other thing is to use a good quality drill that you trust to have been ground accurately. The problem with soft aluminium is it tends to clog the flutes which in turn scores inside the hole. Not the best formula for true running.
31 October 2011 at 09:07 #77099
colin hawes
Participant
@colinhawes85982
Using a slot drill to correct concentricity of the pilot hole will improve the chances of a larger drill to correct any initial inaccuracy as it will then be guided by it’s diameter rather than it’s point or pilot hole.

Colin
31 October 2011 at 09:40 #77101
Richard Parsons
Participant
@richardparsons61721
A 5.5 mm hole drilled 75mm deep. That is a job for a Nug drill (the spelling mistake is quite deliberate). There was a discussion a few months ago on this site about them. Even then the hole will not be true. It will tend to be a curve and this has to be straightened. This was done ‘by eye’ looking down the hole at a window with good daylight and bopping the thing with a mallet or in a press. This process was written up in ME in the past 2 years.

The drill its self had a flat at its business end with a diamond shaped cutting edge. It had a groove or a flat along its length to take the swaff. If you are peck drilling you can get away with without pumping oil down a separate channel, but a hypodermic syringe and a thin length of plastic pipe is a good idea. Use it to flush out the swaff. Hold the work piece so that all of it is between the chuck and the tailstock.

The second method is to rough drill a hole and then use a Greener tool. This is a shaft with a ‘V’ shaped tool with two cutting edges on one end. The shaft is threaded up the hole and held in the chuck. The other end of the thing you are machining is held in a gimble so that the tube can ‘flap about’ but not turn. Greener used a trunnion and chains for this. The cutter is rotated and the work piece is pulled slowly down the tool. Greener used weights for this purpose. Greener claimed it drilled a perfect hole. He would then machine the outside to size.
Rdgs

Dick
31 October 2011 at 11:10 #77108
Ramon Wilson
Participant
@ramonwilson3
Hi Clive, yes understand perfectly – that’s when you really have to compromise

One of the biggest advantages of the Super 7 over the 7 I guess but then I hardly ever changed up to top speed range – different now with the VFD though.

Steves gone quiet – has he drilled his hole successfully I wonder

Regards – Ramon
31 October 2011 at 12:50 #77113
Steve Withnell
Participant
@stevewithnell34426
Just ordering some drills…

I’ve been pondering if I can actually reverse the workpiece accurately and I think it may be possible as the hole has a flat reference surface related to it. So I think the next test run will be to drill the hole on the mill, using a carbide drill. If that is still off, then I’ll try another test piece and drill halfway and reverse the part. The mill will run upto 2500 (my lathe can beat that…) but the real part will have to be bolted to angle plate on the face plate, so the speed will be way less than that – the fixture is static on the mill, so I think that is where the machining should be done.

I will report back after the new carbide has arrived…

Steve
31 October 2011 at 13:15 #77114
chris stephens
Participant
@chrisstephens63393
Hi Guys,

For all you speed freaks, who think the books are right about drilling speeds, you might be surprised how slow you can drill. There is some merit in the thought that you should drill at speeds that allows the lips to cut and not just rub.

chriStephens
31 October 2011 at 13:44 #77116
The Merry Miller
Participant
@themerrymiller
That’s very true Chris, especially when using large hand operated ratchet drills (shades of the 1950’s)

Len P.
31 October 2011 at 16:13 #77126
Versaboss
Participant
@versaboss
Posted by Richard Parsons on 31/10/2011 09:40:27:

The second method is to rough drill a hole and then use a Greener tool. This is a shaft with a ‘V’ shaped tool with two cutting edges on one end. The shaft is threaded up the hole and held in the chuck. The other end of the thing you are machining is held in a gimble so that the tube can ‘flap about’ but not turn. Greener used a trunnion and chains for this. The cutter is rotated and the work piece is pulled slowly down the tool. Greener used weights for this purpose. Greener claimed it drilled a perfect hole. He would then machine the outside to size.
Rdgs

Dick

Dick, would it be possible to show a sketch of that Greener tool? I admit having trouble to visualizing this from your description. Google just brings up a lot of ‘greener ways to drill for oil’, not what we do here?

Greetings, Hansrudolf
31 October 2011 at 16:53 #77129
Donald Wittmann
Participant
@donaldwittmann92536
Steve,

Your drilling is maybe not at fault, The problem could well be that your chuck jaws are not holding the part true to the lathe bed. Even if you set the outer end to a couple of microns the inner end that projects to the rear of the chuck could well be off with the result that the hole [even if it is true] would be eccentric to the outer Ø.

So you should also check your chuck / chuck jaws.

Donald.
5 February 2022 at 16:31 #584008
Buffer
Participant
@buffer
Hi All

I need to drill a 14mm hole 300mm deep right through a bar 60mm diameter of EN1A steel.

It doesn't need to be precisely on centre as I will probably turn between centres at the end.

I was going to hold it in the four jaw with the fixed steady and then drill and bore a hole to get the drill off to a good start. Then just go at it for the day with a HSS jobber drill and extend it when I need to. Has anyone done this sort of thing before and got any advice or top tips before I get to work? I was wondering about things like maybe drilling it a little under size and finishing with a D bit for example. The finish needs to be reasonably good but not brilliant.

Many Thanks.

Edited By Buffer on 05/02/2022 16:36:41
5 February 2022 at 16:57 #584011
Anonymous
When I needed a 1/2" hole through 250mm of EN1A I centre drilled, started the hole with a 12mm stub drill, then a jobbers drill and finally an extra long jobbers drill. Lastly I reamed with a 1/2" long series reamer as I needed a good finish.

Andrew
5 February 2022 at 17:35 #584015
Buffer
Participant
@buffer
Thanks Andrew. I presume this was in the lathe and not the mill as you suggested above? Did the drill stay centred ok at the other end? I guess it would do being a 1/2 inch.
5 February 2022 at 18:42 #584024
Anonymous
Posted by Buffer on 05/02/2022 17:35:35:

…I presume this was in the lathe…

Correct, it was done on the lathe. My mill didn't have enough headroom. The part has a cover on the end with a short 1/2" spigot. The OD of both part and cover are stock size. I can just feel a slight ridge between the cover and part. So I guess the runout of the hole is around 0.1mm or so.

Andrew
5 February 2022 at 19:27 #584031
Andrew Crow
Participant
@andrewcrow91475
Most drills wander slightly caused by various factors and exacerbated as the hole is drilled deeper. The best way I have found to keep the hole true is to start with a centre or starter drill followed by a drill about 1/32 under finished size then bore the hole to just under the next drill size that will leave a few thou for reaming. Bore as deep as possible, follow up with the next drill ( at a reduced speed, about half normal drilling speed) which should follow the bored hole then finally use the reamer. It sounds a bit laborious but does work.
6 February 2022 at 00:33 #584078
Emgee
Participant
@emgee
The Eric Whittle designed V8 engine posed a very similar problem, a 7/32" reamed hole through the 75mm long crankcase, Eric did his drilling and reaming on the lathe with the material held in a Keats angle plate at the desired offset for the camshaft gear.

He does advise to have the gear end of the crankcase at the tailstock end to ensure the gear will be be correctly positioned to mesh with the driving gear, any runout of the camshaft centre will effect the valve openings but that's of less importance than the gear centre distances.

Emgee
6 February 2022 at 01:29 #584082
pgk pgk
Participant
@pgkpgk17461
Surely the approach depends on the purpose of the hole? One option might be to drill undersize each end then take a 14mm carbide endmill to size from each end (or ream a distance from each end) and bore the centre section oversize?
I've never used them but gun drills sound like the 'correct' way.

pgk
6 February 2022 at 07:51 #584093
David George 1
Participant
@davidgeorge1
Hi I have used gun drills and they need the hole to have a good start. The hole follows the original start usually 20mm deep ish and hole is started with a cutter not a drill which is a few thou smaller than a gun drill. A gun drill is a carbide piece about 20mm long on a steel shaft only has one cutting edge and the other side is just round and clearance on the front. It just cutts on the one cutting edge and runs on the other side diamiter. There is a straight groove down the length to allow the chipings to exit to the rear and a hole down the center for coolant lubricant oil under pressure to also flush out the swarf.

If you want a drill to run straight the start hole must run straight in a home workshop I would recommend two stage drilling. Center drill both ends and drill out from both ends with a smaller drill firstly. Then bore the end to the same diamiter as finnished drill size at least 20mm deep, which may be a reaming size. Then either drill through if the drill is long enough or repeat from other end to join up. This is how I get true holes now I don't have access to gun drill machine.

David
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