Boring a Cylinder

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Boring a Cylinder

This topic has 28 replies, 10 voices, and was last updated 8 January 2011 at 07:49 by JasonB.

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5 January 2011 at 17:43 #5348
Hugh Gilhespie
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@hughgilhespie56163
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5 January 2011 at 17:43 #61801
Hugh Gilhespie
Participant
@hughgilhespie56163
I am about to take a big step (for me) and make my first cylinder. I have read up quite a lot about boring cylinders, in fact too much and I am now at the confused stage.

The cylinder itself is a squarish lump of bronze, Colphos I think, and needs a 1 inch bore around 2 inches long. I have two basic options for making the bore. Either I can drill and ream or bore and ream or some combination of the two methods.

I was fortunate that when I bought my mill it came with a goodly selection of fairly hefty tooling and I have found a 25 mm drill and a 1.01 inch machine reamer, both on MT taper stubs that will work nicely as a pair if I drill.

Basic plan is to use the lathe for whichever method I use as that means I can face at least on end of the piece truly at right angles to the bore.

I intend to lap the bore after machining as I will be using a Viton ‘O’ ring rather than cast iron rings and I understand that a polished bore is better than a honed one for the rubber seal.

So, could some helpful people give me a heads up on the pros and cons of drilling versus boring? I am keen to avoid a tapered bore and at the present I am leaning towards drilling.

Also, please, can you help me with what sort of lapping compound to use? I have not done this before so I’m a bit at sea.

Thanks in anticipation.

Regards, Hugh
5 January 2011 at 18:01 #61805
JasonB
Moderator
@jasonb
The disadvantage of drilling then reaming is that the drill is likely to wander and the reamer will just follow the drilled hole so you can end up with a reamed hole that is out of line with your faced end. A bored and then reamed hole will be truer.

I would drill out as much as possible depending on what other drills you have upto 7/8″ bearing in mind bronze is not the easiest to drill so maybe 1/2″ would be safer. Then switch to a boring bar and bore to 0.998″ and the lap to 1″ as you are unlikely to get 1.010″ virton rings and a 1″ ring is designed to fit a 1″ hole.

Something like brasso for the lapping compound a sanything more abrasive like valve grinding paste or diamond paste may get imbedded in the bronze.

Jason

Edited By JasonB on 05/01/2011 18:02:58
5 January 2011 at 18:05 #61806
Ramon Wilson
Participant
@ramonwilson3
Hugh,

Finishing a bore by drilling and/or reaming alone is not a good idea – the size will in all probability be fine but the finish is not always guaranteed. You will see the evidence of this when you begin lapping and the less you have to lap the more control you have of keeping the bore parallel.

It would be much better to bore this out to size making sure the tool is razor sharp before the final few cuts. Boring from one end to ensure one end is square is fine but can – sometimes – lead to a taper bore even after taking several passes at the same setting. If possible – to guarantee a paralle bore – the best method is to use a between centres boring bar. The ends of the cylinder can then be brought square using a easily made expanding mandrel held in the chuck. This also enables any machining on the outside to be carried out relative to the bore.

I haven’t lapped bronze of any size as yet (the odd I/C motor big end 6-7mm dia) but have used silicon carbide without problem – I would use an ally lap – the better the finish the less on this op the better

Hope this helps enough – I’m sure others will add more. Just keep asking till you are happy you have sufficient info before machining that expensive lump of bronze

Good luck with it, however you go about it

Regards – Ramon

Edited By Ramon Wilson on 05/01/2011 18:07:31
5 January 2011 at 18:12 #61809
Ramon Wilson
Participant
@ramonwilson3
Just an add on Hugh.

You may already be aware but just in case — If it is Colphos you shouldn’t have too much of a problem but phosy bronze can work harden, particularly when drilling, very quickly indeed – the tools must be sharp and they need to be kept ‘cutting’.

Hope that’s not teaching granny

Ramon
5 January 2011 at 18:39 #61811
John Olsen
Participant
@johnolsen79199
I would agree with Ramon and Jason, and would further mentione that when you are drilling the initial holes, the drill is likely to want to grab with any of the bronze materials. Apart from the trauma involved, and the risk of the job moving, this is best avoided. It is especially a problem when you have run a smaller drill through and are opening out with a larger one, or at the moment when the drill breaks through. In either case, the drill no longer has the chisel point to hold it back, so the rake on the cutting edge will tend to pull it into the job.

The way to avoid this is to modify the drill so that it has no rake on the cutting edge. This can be done with a small stone. The edge should be either zero rake, or even a slight positive rake. Of course having done this, the drill is no longer ideal for other materials, so you really want a few duplicate sizes for this sort of thing. Note that although the rake is no longer negative, the edge should still be very sharp.

regards

John
5 January 2011 at 19:01 #61814
JasonB
Moderator
@jasonb
John have you got your posative & negative the wrong way round?

A standard jobber drill will come with positive rake and you stone it back to zero or negative

J
6 January 2011 at 00:43 #61830
ady
Participant
@ady
I do know that with drills you have to skim the end of the drill flutes, to stop them expanding in the cut, and this creates an accurate cut while the following flute spiral generate a reaming action.

It makes a weird noise, but creates a good accurate hole.

On the flip side, I seem to recall someone like Mr Sparey saying don’t rub down the flutes with a couple of workpiece materials or the drill will jam tight, and one of them might well be bronze…

I looked it up, never do it with copper or phosphor bronze because they tend to bind.

A bit of a pain where PB is concerned, since it can be used for bearings.

Bronze and copper appear to not need stoning off according to monsuier sparey.

(p87 the amateurs lathe.)

Edited By ady on 06/01/2011 00:50:42
6 January 2011 at 01:46 #61831
John Olsen
Participant
@johnolsen79199
Yes, I am confusing myself I guess. Wrong way around. Sorry about that!

It is not so much the flutes we are trying to modify, it is the cutting edge.

regards

John
6 January 2011 at 08:54 #61833
Ramon Wilson
Participant
@ramonwilson3
Just to add a bit more to poor Hugh’s confusion don’t get too diverted in the need to stone the tips off.

This is not to dismiss or disagree with what other advice has been offered because I totally agree with this principle in most brasses as without it the drill will grab and pull itself in quite alarmingly and particularly when opening up a previously drilled hole.

However with phosphor bronze the important thing is to keep it cutting – if it rubs it will harden very quickly and take the edge off the cutter just as quick – heat generates at an alarming rate and the drill can get well and truly stuck. It then needs a very sharp tool to get under the skin at slow speed before starting again – if he job isn’t ruined that is

The thing with PB is to be careful but confident. Once you have a hole large enough it’s much better to bore it than drill it IMO.

This does depend on the type of phos bronze though. Hugh said he thought it might be Colphos which is free cutting so should not present such a problem but if it’s not but is drawn PB then hardening is potentially on the cards and something to be wary of

Regards – Ramon
6 January 2011 at 09:48 #61835
Dusty
Participant
@dusty
Hugh

Do not put a reamer anywhere near the bore of a cylinder. A reamer is a sizing tool and is not meant to produce the sort of finish required on a cylinder bore.Secondly as has been stated when drilling, the tool will have a tendency to snatch(in this case the reamer) this will cause minute flats within the bore, you may not even see them by eye. The end result can be a hole that looks like a 50p piece. To reduce the the potential of a tappered bore make sure the lathe is adjusted properly (no slack in any gib) reduce the overhang of the boring bar, making sure the topslide is withdrawn, and most important set the tool on centre height.
6 January 2011 at 10:43 #61837
Hugh Gilhespie
Participant
@hughgilhespie56163
Thank you for the advice. I will go with boring out rather than drilling. Of course, I have to drill first to get a hole big enough for the boring tool and as I want to use my 16 mm boring bar, this means drilling up to about 20 mm.

Now I am suitably terrified about the drills snatching! It occurs to me that there is a risk of the drill chuck (or drill MT2 shank for the big’uns) being pulled out of the tailstock. Maybe I should have gone for a cast iron cylinder! I did check on the bronze I have from M-Machine Metals and it’s called ‘continuously cast leaded gunmetal’. Not Colphos 90 but hopefully not too difficult to machine.

A bit alarmed at Dusty’s advice not to use a reamer. I will of course do everything I can to get a non-tapered hole but the final reaming was my ultimate answer to oval, taper and actual size. I have to confess to being pants at actually measuring internal bores. I only have the spring loaded thingies and the best I can get in terms of repeatable readings is plus or minus 1 thou. I spent hours taking literally hundreds of measurements on a test bore trying to improve my technique. I would take 12 separate readings each time, discard the highest and lowest then get the RMS deviation. I did get this down from 3 thou but plus or minus 1 thou is the best I can do. So, taking Jason’s point about needing to bore to size to suit the O-ring, I’m a bit stuffed anyway. On this point can someone be kind enough to tell me where to find info on what size groove I need for an O-ring?

So, still confused but I guess the thing to do is just have a go! All the theory in the world doesn’t actually produce anything.

Thanks, Hugh
6 January 2011 at 11:03 #61838
ady
Participant
@ady
Good lapping and honing techniques will be skills unto themselves.

Grinding, Lapping and Honing (Past Masters)

Edgar T. Westbury (Author)

http://www.amazon.co.uk/Grinding-Lapping-Honing-Past-Masters/dp/0905100689

…so much to learn…so little time to learn it…
6 January 2011 at 11:36 #61842
ady
Participant
@ady
I knew I’d find something eventually…

Sparey, p187 The amateurs lathe.

The “Delapena” portable adjustable honing kit can do internal and external honing to 0.0001 inch in the hands of a semi skilled operator.

They appear to use a solid honing block in a holder.

Probably no longer sold, but will give you some pointers.

gl

Edited By ady on 06/01/2011 11:38:14
6 January 2011 at 11:51 #61845
ady
Participant
@ady
How weird, my later edition of Spareys book no longer mentions the Delapena unit.
6 January 2011 at 11:55 #61846
KWIL
Participant
@kwil
You could pratice on a piece of brass or ali, much cheaper than PB/GM!
6 January 2011 at 12:18 #61847
Jeff Dayman
Participant
@jeffdayman43397
I’ve use a reamer on several steam engine cylinders without any trouble. However this is likely due to using good quality reamers. If you have a badly drilled hole and a poorly made cheapie reamer you will not likely get a good bore.

However all that said, boring between centres and then lapping will likely give you best chance at an excellent cylinder as others have said. I recall that College Engineering Supply sold inside and outside lapping tools and stones at one time, maybe they still do.

Be careful to use a lapping compound intended for bronzes, or it may embed into the cylinder wall and abrade your Viton ring later. Wash the compound out really well, then wash it out again, repeat.

I have made some successful “emergency repair” laps for hydraulic and small engine work from rock maple wood and elm. Any hard wood will do. Split the wood like an ER collet partway down the length from either end in several places and fit tapered cones in both ends to expand it gradually, and keep an eye on the bore, measuring frequently to ensure you don’t get taper.

Doing a test piece or two would be a good idea before going for it on your best bronze block.

JD
6 January 2011 at 12:21 #61848
Ramon Wilson
Participant
@ramonwilson3
Hi Hugh,

Lets take this one stage at a time.

First off is the bronze you have should not exhibit the work hardening tendency that I have described

.

Reaming will give you a good size but as said no guarantee of finish and you will get the ribbing also described but this will only become noticeable when lapping.

Lapping should only remove the minimum amount of material so a bored finish is definitely to be preferred before lapping.

Drills really snatch when you are not paying attention

I find that the slight stoning described – not much is required, just a narrow 5 thou or so – coupled with applying a slight tension on to the tailstock barrell using the lock and a gentle but steady application does the trick. Don’t be tempted to use too many steps to get to the desired hole size. Taking small amounts will increase the likelyhood of grabbing. Be particularly care ful as you break through.

Measuring – The spring loaded plunger type of internal measuring are fine however you may have this problem.

Originally I had a small set of Moore and Wright which had one fixed and one moving plunger. These gave very consistent readings. I bought a cheaper set with larger range of the double plunger type and these gave very much the opposite!. I took them all apart and stoned and polished all mating faces which improved their consistancy considerably – maybe worth a try.

If you are unfamiliar with using these… Set the plunger(s) by eye with a light nip of the lock outside the bore so that it has to be held at an angle to enter the bore. (You can do this inside the bore too but make sure its at an angle) Move the whole through an arc so that the pressure closes the plungers against the lock pressure – go over centre and then remove. Don’t be tempted to reverse or do it twice but reset each time. To measure hold one plunger to the mic anvil and swing the other through an arc closing the mic until the mic just stops it – this will give a very accurate reading withing the limits of this particular method of internal measuring but it does take a bit of practice.

With regard to the ‘O’ ring. I have tried this method but found the tolerances to get a nice sliding fit are very fine. Most info on O ring grooves are for their use as a seal but will give you a guide. I have that info if you wish – PM me with the sizes and I’ll copy it for you

You don’t say what this cylinder is for – if it’s for a stationary engine personally I would fit PTFE impregnated yarn but that’s just my preference.

Hope this helps a bit more

Regards – Ramon

Edited By Ramon Wilson on 06/01/2011 12:24:55
6 January 2011 at 12:39 #61851
Ramon Wilson
Participant
@ramonwilson3
Hugh,

For what its worth I have just found this pic which may be of interest.

This is a cylinder for a table engine which is made from solid. All the outer ops were done to the bore using the expanding mandrel – in this instance it has been transfered from lathe chuck to angle plate on the mill.

Just thought that it might help – but hopefully not – to add to the confusion

Regards – Ramon

Why is it you can never see the mistakes until after it’s posted

Edited By Ramon Wilson on 06/01/2011 12:41:12
7 January 2011 at 10:12 #61906
Ian S C
Participant
@iansc
    For lapping cylinders I use wooden cylinders split lengthwise with a screw or wedge in the split. Most of my cylinders are steel, so I use ordenry grinding paste, but for bronze Timesaver would be best, as it breaks down rather than imbeds in the work. Brasso is good if you have very little to remove.

    I’m afraid my cylinders ar’nt allways perfect(by a long way), so a break cylinder hone is some times used to sort things out. Another way that can work for a rough start is a wooden dowel (say 1/2″ dia), with a slot cut lenghwise in one end, this is to take a short length of carborundum cloth. Put the other end in the chuck on the drill press, and with the carborundum cloth in the cylinder, start the drill and work the cylinder up and down, watch it, it removes metal quite fast, maybe best for steel or cast iron, never tried on bronze.

    Unless you have a spiral reamer, you may end up with longitudinal corrigations, they will show up when you start lapping.   Ian S C
7 January 2011 at 11:00 #61909
ady
Participant
@ady
Brake cylinder hones look interesting.

Are they pretty easy to use and give decent results?

hones
7 January 2011 at 11:22 #61910
ady
Participant
@ady
One here does 13-64 mm
7 January 2011 at 11:34 #61911
Ramon Wilson
Participant
@ramonwilson3
Ady,

Brake cylinder

hones work well but will not true an out of round bore nor a tapered one. It is also easy to bell mouth the cylinder with them too if not done with care.

They are ideal for putting micro ‘scratches’ into the surface of the bore for oil retention.

It is much better to make a lap for truing the bore – in most home workshops that is.

Regards – Ramon
7 January 2011 at 11:56 #61913
JasonB
Moderator
@jasonb
One other problem with the cylinder hones is that the cross hatch pattern they produce will be far too coarse for the Vitron O rings and will quickly ware them away.

They are ideal for CI cylinders with CI rings though and easy to use. This is one of mine in action only the other week.

J
7 January 2011 at 12:36 #61917
Brian Everett 1
Participant
@brianeverett1
Just a suggestion. Having completed your boring and lapping process to your satisfaction, if you are uncertain of the accuracy of your faced ends to the cylinder, chuck a scrap piece of material, well seasoned hard wood would do it, and turn a full length mandrel to be a press fit in the cylinder bore.

If there is enough interference fit you should not need to hold it further, mark the ends with engineers blue, or even felt tip pen will do, then, while rotating it at relatively slow speed, skim the end faces with extremely fine cuts till they are continuous and the marking gone, that way they will be guaranteed to be accurate.

Good luck with your project.
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