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Boring problems
| Howard Sutcliffe | 29/09/2010 10:06:43 |
| 11 forum posts | I recently finished making a Stuart Victoria engine and, although it’s taken me a long time, it looks as if it will work alright – if I’m not tempting providence by saying that! However, I’m now getting more and more annoyed with myself whilst making its governor. The part that’s defeating me, no doubt due to my lack of experience, is the tube component of the spindle assembly. As supplied this brass part is 2 1/2 inches long, with OD of 3/16 inch and ID of about 3/32 inch. The finished piece is to be 2 1/4 inches long, threaded 3/16 inch x 40 tpi at each end and bored out to 1/8 inch to take a stainless steel rod.
In consideration of the final thin walls, it seemed best to thread the ends first and then to bore out. I had no small, long drills and bought some of various sizes up to 1/8 inch to enable me to enlarge the bore gradually. I started by centre drilling the end to persuade the drill to centre itself initially, but on each of my three attempts at boring out pieces of tube the left end of the bore has ended up off-centre. On one occasion it was so far off that the bore broke out of the threaded side of the tube, although I was blissfully unaware of this until I removed it from the lathe chuck.
What am I doing wrong? Over the years I’ve learned gradually from making many mistakes, but this is defeating me. I’m using about 700 rpm – should it be more (or less) for this task? I’d be grateful for any advice or tips to enable me to tackle successfully this part of the job. Edited By Mark Web Tech on 29/09/2010 10:37:56 |
| Ian S C | 29/09/2010 10:48:19 |
 7468 forum posts 230 photos | Hi Howard, one I'd say 700rpm's OK but if you have more go for it. I would use an ordenary size drill, adn drill just over half way from each end, i'd have thought that the drill would follow the hole already there, but I'd still go in at each end. Ian S C |
| Andrew Johnston | 29/09/2010 11:39:28 |
 7061 forum posts 719 photos | If I understand correctly the part is supplied with a 3/32" bore already existing? Any drill will tend to follow the existing hole. I'd start with a stub drill (ideally carbide), or a D bit, to provide a true start to the hole. Then a normal drill. Drilling from both ends should be ok, and saves buying a long series drill. However, it will depend upon the accuracy of your chucking arrangements. If, upon turning the part end for end, it doesn't run on the same axis, one cannot expect the hole to then be true. Running at 700rpm is fine, although personally I'd probably run double that. Use quality drills, I use Dormer; if the drill isn't ground correctly in the first place it isn't going to drill true. Regards, Andrew |
| David Clark 1 | 29/09/2010 12:09:28 |
 3357 forum posts 112 photos 10 articles | Hi There
As the hole is already 3/32, can you turn down the shaft to fit the hole.
Might be a lot easier.
regards David
|
| Lawrie Alush-Jaggs | 29/09/2010 14:47:22 |
 118 forum posts 32 photos | Hi Howard
As Andrew says, a D bit will cut an accurate hole.
I would not use one though, I'd just go out and buy a 1/8 long series drill, carefully grind the cutting lip almost flat as should be done for brass and then run it at 3,000 RPMs, the reccommended speed for 1/8 in brass.
You use the term boring when you are talking about drilling. The two are not the same. Boring in engineering terms is the process of accurately enlarging an existing hole. Drilling is the process of creating one.
You don't mention wether you are trying to perform this operation in a drill or a lathe.
If you are doing it in a drill then I can understand why you are drilling off centre, especially if you haven't prepared the drill bit for brass AND you are running at 700RPM.
It is almost impossible to drill a hole at that speed with that sized bit in a vertical drill.
If you are trying to do it in a lathe and you know the tailstock is accurate in relation to the spindle, then it is the speed and drill that are your problem. Otherwise sort out the lathe first. |
| Dinosaur Engineer | 29/09/2010 16:44:03 |
| 147 forum posts 4 photos | It may be that your tailstock / drill chuck is not aligned or is running out.
You could check the drill chuck by running it in the headstock taper and check the run-out with a piece of straight silver steel or long dowel in the chuck. The cheaper drill chucks are some times not as accurate as you might like to think. Check the taper in the tailstock has no internal burrs or gouges.. A session of bluing/scraping the tailstock barrel taper with a mating morse taper shank may be required to remove any high spots or clean up with a morse taper reamer if you have one You would of course need to remove the tailstock barrel to scrape it. This would be difficult to scrape or grind with small stone (Dremel ?) in the smaller taper sizes due to access/visiblity. Also check the tailstock alignment with the headstock.Ideally check the tailstock morse taper centre with a magnetic stand DTI set on the headstock faceplate ( the faceplate needs to flat & square to the spindle for this check ). Or check alignment by the time honoured way of turning a longish bar ( with two collars) and checking for parallelism. A check of the parallelism of the tailstock with the bed over the full tailstock travel should be made . You could check the drill chuck/tailstock parallelism alignment with a longish piece of silver steel in the chuck with chuck in the tailstock against DTI held on saddle/crosslide/topslide. A test bar with a matching morse taper to the smallest taper in the lathe ( usually the tailstock) can quickly highlight alignment problems. Hardened morse taper test bars, centred each end , are available from about £40. Maybe a friend has the necessary equipment to do these checks for you ? It doesn't take long with the right equipment.
Fixing the problems might take a lot longer ! My guess is that your drill chuck is running out if everthing else is O.K. You only need to stone a small flat on each drill cutting edge to stop it "grabbing" when drilling brass.
I know this sounds a little complicated but if you are unsure, then Sparey's ( spelling ?) "The Amateur's lathe" book would help - local library ? |
| Steve Garnett | 29/09/2010 17:10:36 |
| 837 forum posts 27 photos | Posted by Lawrie Alush-Jaggs on 29/09/2010 14:47:22: You don't mention wether you are trying to perform this operation in a drill or a lathe. Oh, I think he did - end of para 2. My own experience of trying to bore out existing holes in thin-walled tube with a drill is that you have to take some sensible precautions. For instance, be
prepared to slide the tube through the chuck so that at any time, the
drill you are using is drilling into a part of the tube that's
completely supported by the jaws - then pull the drill out, move the
tube forward and drill the next bit. Or, support the tube with a fixed steady. Have the minimum amount of drill
protruding from the tailstock as you can get away with, withdraw it
often and lubricate well. And that's after doing the stuff that Dinosaur Engineer suggested to your tailstock...Then the whole thing might stay aligned - if
you don't do this, a lot of the tube you are drilling is unsupported,
and being that thin, anything could (and probably will) happen. And as others have mentioned, it's brass - so prepare the drill. |
| Dinosaur Engineer | 29/09/2010 17:39:29 |
| 147 forum posts 4 photos | If the tube is being distorted by using a 3 jaw chuck then it might be better to hold it in a pre-prepared 'C'' section round bar with the inside of the 'C' section bored / drilled / reamed to fit the part O.D. This would give much more support to the part O.D. and minimse any distortion . Obviously a collet would be preferable but if you do not have a collet then make one. Make sure the 'C' section slot edges are de-burred. Mark the home made collet before slotting and removal from chuck with the chuck jaw # 1 position and replace in this postion after slotting ( hacksaw ?). This will minimise any chuck run-out influence although the 'C' section will most probably "spring" after slotting. Use hot rolled mild steel bar for the collet if you have any and turn collet O.D. to good finish. Hot rolled M.S. will reduce the "spring" when slot is cut. Don't overtighten the chuck. |
| Dusty | 29/09/2010 17:56:50 |
| 498 forum posts 9 photos | Howard
I am going to fly in the face of everything that has been suggested so far. The biggest problem is crushing the tube in the chuck jaws, if you have a collet this will overcome to a degree that problem.As this appears to be brass tube it is not going to be the usual 60/40 brass and therefore I would not negative rake the drill. Negative raking the drill in this type of brass will cause the drill to try and push the metal rather than cutting it, that will increase the problems you are experiencing. I would not tighten everything up but allow it to float, this way the drill will guide itself, yes do lock the tailstock but do not lock the barrel. First use a 3mm drill (best if this is a new drill) followed by a 3.2mm drill, this drill should be doctored by grinding a small radius on the two corners of the drill, this can be done freehand. If you feed this fairly slowly you will get a good finish, generally better than a reamer as the drill will cut as opposed to scrape. You will still need to be aware of the drill snatching but it is far less likely than with 60/40 brass. |
| Steve Garnett | 29/09/2010 18:22:24 |
| 837 forum posts 27 photos | Posted by Dusty on 29/09/2010 17:56:50: .... you will get a good finish, generally better than a reamer as the drill will cut as opposed to scrape. You will still need to be aware of the drill snatching but it is far less likely than with 60/40 brass. Dusty, that sounds like a recipe for problems. For a start, a proper reamer doesn't scrape at all - it very clearly cuts, and the results on all forms of brass are good. I don't normally quote Wikipedia if I can avoid it, but they do have one useful thing to say about reaming that's directly relevant to this situation: "Reaming removes a very thin layer of stressed and disturbed material caused by drilling a hole." And in this instance, this is particularly relevant because we are talking about a thin-walled tube being cut by a drill with just two flutes, and this is much more likely to deform marginally than a lot of material - which is why I suggested reaming in the first place - the distortion is far less likely to occur. |
| Dusty | 29/09/2010 19:50:14 |
| 498 forum posts 9 photos | Hi Steve
Whilst I will not take issue with you on the fact that a reamer cuts. Unless you have a machine reamer long enough to pass through the job (I doubt most model engineers will have) a hand reamer cuts on such a wide front that the forces involved are such that you would never hold a thin walled tube, except in a collet , without it collapsing, tight enough to stop it turning. A 'D' bit is another proposition.
With care my method will work. |
| Steve Garnett | 29/09/2010 20:50:26 |
| 837 forum posts 27 photos | I agree entirely about the collet - but this is only a short tube, and you could run a reamer in from both ends - RGD do suitable ones pretty cheaply. |
| Dusty | 30/09/2010 13:05:27 |
| 498 forum posts 9 photos | Howard
Having re-read your original post I notice that you have had several attempts at this component. You are obviously not using the original material, what are you using? If you are using brass bar and drilling the hole from scratch this may be part of your problem. Drilling long thin holes in the lathe is problematic in as much as the drill has a tendency to wander. This has something to do with rotating the work round the drill. I did know all the reasons why this happens, but the passage of time has dulled my memory. If I were doing this job I would start with a bar of say 1/4" dia and about 3/4" longer than the finished job. Drill the hole, if using 60/40 brass then yes negative rake the drill, use a new good quality drill and as big as you dare, 3mm? and finish to size. Reaming from both ends is not good engineering practice, if you are going to ream do it from one end only. Now mount the job between centres and turn the outside to size. Screwcut the first end and remove. cut to length + allowance for cleaning up. You can now put a short length of 1/8" dia into the hole and mount in the 3 jaw or collet, make sure that it is running true screw cut the other end having finished to length you can just run a die down the thread to finish it. Reverse and die the other end if required. Job done. |
| Dusty | 30/09/2010 17:26:12 |
| 498 forum posts 9 photos | Howard
To prove to myself that I was not talking a load of b******s, I have just spent 40mins in my workshop and created your component from scratch. Using my method above. If I knew how to put photo's on the system I would show you. I used a 3/32" long series drill followed by 1/8" long series the lathe was run at 1600rpm for the drilling and the turning
It does work! And for information the 3/32" hole was only 2 1/2 thou off centre. Edited By Dusty on 30/09/2010 17:49:14 |
| Dusty | 30/09/2010 18:11:12 |
| 498 forum posts 9 photos | I have sussed out how to add photos, sorry about the quality, the rule is a 6". I will now have to learn how to take decent photo's. |
| Steve Garnett | 30/09/2010 20:03:47 |
| 837 forum posts 27 photos | Posted by Dusty on 30/09/2010 13:05:27: Reaming from both ends is not good engineering practice, if you are going to ream do it from one end only. I wasn't claiming that it was good engineering practice - but on a small part with considerable overlap available, it would work fine on this particular job.
|
| Howard Jones | 01/10/2010 10:19:59 |
| 70 forum posts 112 photos | howard the easiest way to the final solution is to ply dusty with grog for the effort and arrange to have the bit he made posted to you. ...that is another way of doing it. another Howard |
| Nicholas Farr | 01/10/2010 11:28:08 |
 3988 forum posts 1799 photos | Hi, "not good engineering practice" Well maybe not, certanly not on production lines. I would imagine that most of us are giulty of performing this in our home workshops, as our resoures and bugets don't stretch as far as the commercial world for the majority of us. We accomnodate items onto our machines with adaptions sometimes, beyond thier design limits, use our machines in an unconventual manner etc. As long as we bear in mind our personal safety and anyone else who may be involed in our activity, what does it matter. If you get the result that you reqiure in a time frame and cost that suits yourself using a bit of innovation, I would say it is acceptable engineering at the very least. QED.
Regards Nick |
| Howard Sutcliffe | 03/10/2010 14:35:10 |
| 11 forum posts |
Many thanks to all for the advice and tips in response to my original post. Dusty – to answer your question - after my initial problems I obtained some more pieces of the original tubing. After viewing your photo, I realised that I forgot to mention that the finished tube (2¼ inches long, 3/16 OD, 1/8 bore) is threaded 40 TPI for 1¼ inches at one end and 3/16 inch at the other, leaving only 13/16 inch unthreaded. After I’d die-threaded each end of the original plain tube, it seemed to me that I wouldn’t be able to grip it for boring out in the lathe chuck without the certainty of damaging the threads. I decided to hold the threaded brass tube in some thin walled, 3/16 inch bore aluminium tube, slit lengthwise. This did protect the threaded portions, but the final bore had the problems I described initially. Before trying once more, I’ve bought some new drills including 1/16 and 3/32 stub and 1/8 inch slow spiral (apparently recommended for brass), although I’m not sure of the rpm to use with this one. I think I’m going
to try reversing the tube in the chuck (as suggested by Ian S
C and Andrew Johnston) and bore it out at higher speed, so I thought I’d best re-check my 30 year old Super 7’s
alignments, as brought to mind by Dinosaur Engineer’s comments. Using my 2MT test bar I got the following
results on the bar’s 4½ inch long parallel with my tdi on the cross slide:- In headstock taper
– tdi on front side of bar facing me, zero out end to end - I appreciate this only means undetectable with my tdi. Rotating spindle by hand - about 1/5 thou out
at the right end, zero out at left end.
With tdi on top of bar, ½ thou out end to end – I’d not thought of checking
this previously. In tailstock taper – zero out end to end. Test bar held between centres in headstock and tailstock – zero out on front or top of parallel. Headstock spindle register face – zero out. Test bar gripped by part of its parallel in lathe chuck – about 2 thou out end to end; rotated by hand – 3 thou out near chuck, 5 thou out right end. Length of silver
steel – 12 inch – held by tip of lathe chuck and tailstock chuck - ½ thou out
end to end. I don’t have figures for Super 7 tolerances, but the results
seem acceptable to me, with the exception of the lathe chuck test. I’ll check the backplate and perhaps re-machine
it. The headstock spindle appears not
quite parallel with the lathe bed; but is ½ thou out in 4½ inches sufficient to consider
shimming the headstock?
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