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Post by Roger on Mar 22, 2019 20:46:43 GMT
Clipped for clarity, Roger wrote "I don't think you would get even close to what's achieved on a PCB drill sharpening machine, even with a tool and cutter grinder, let alone by hand! We're talking about exquisitely ground micro-grain carbide here, it's in a different league to most commercial general purpose drills. They cost around £1 a piece, why would you want to sharpen something by hand and risk scrapping the job?"It is because most of us know nothing of PCB carbide drills etc and their great advantages. I was ignorant till I learnt from your posts on these forum pages and I then tried them out after buying some via ebay. Yep, I agree with what you say. Brilliant tools. I cannot recall them mentioned in the pages of ME mags etc. So I think it is all that we know after decades of reading these publications and or the handing down of techniques from the senior makers thus the recognition of new approaches/techniques takes time to be outed and then absorbed. If LBSC had carbide PCB drills he would have surely spoken in praise of the them. Hi Daz, I was responding to Rob really, who seemed to imply that you could touch a drill up a tiny HSS by hand and that would be just as good. It's certainly true that MEs seem unaware of PCB drills, even though you can see them on sale at some ME shows. Hopefully Forums like these will spread the word and these useful tools will be spoken about in magazines and they will eventually reach the mainstream.
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Post by ettingtonliam on Mar 22, 2019 23:53:34 GMT
A bit like replaceable tip tooling. I was first shown some by a toolmaker in about 1980, but it was a long time before they became common knowledge in the ME world.
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Post by Cro on Mar 23, 2019 7:51:04 GMT
Thanks to Roger I now have a range of 0.3 all the way up to 1.4 including 0.55 & 1.05 and other odd sizes and use them fairly regularly and in reality they are so cheap they are a no brainer for me.
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Post by 92220 on Mar 23, 2019 10:25:39 GMT
I missed reading this thread for a couple of days. I see there is quite a bit of talk about drilling deep holes accurately. This is how I drill a 3mm hole concentric to within 2 thou over a depth of the drill flutes, in the lathe, and it works with any size drill: First off I buy a brand new British made drill of the size I need. I say 'British' because I understand that the flute angles and corew diameters, of British drills differs from far eastern ones. Also I can be fairly certain of the quality. I use a No.1 centre drill to centre and don't drill so deep as to start the cone cutting. Just because the drill end is not perfect, doesn't matter. The fact that you are drilling into a rotating piece, automatically sets the drill cutting dead centre. That is why it has the name 'Dead Centre'. From this, you might say that if this was true then it should also be true for using a normal drill straight into the workpiece. It doesn't work like that because the length of the drill allows it to wander across the surface BEFORE it actually starts to cut, and if it digs in anywhere other than the dead centre, it will keep cutting from that point.. As long as you have a perfectly centred hole to start with, you can drill deep holes with almost no wander.
The problems would start if the subsequent drill is not ground dead accurate so that the cutting edges are not cutting equal amounts and thus having equal forces acting on them. That's why I would use a brand new drill. Feed the final size drill in slowly, to just start the cut. Back off and take another cut for about 10 thou, back off sand then take another 10 thou cut. Keep taking these small 'bites' with the drill. Make sure there is no build-up of swarfe in the drill flutes, though this is unlikely with such short drilling 'bites'. You should be able to take the drill down to full flute depth and still have a hole that has not wandered more than about a couple of thou. I've done this numerous times with total success, clocked with a piece of silver steel in the resultant hole.
The trick is the very short drilling cuts and the new drill. The reasoning behind this is that a: the new drill should be ground dead accurate, and b: the short 'bites' with the drill don't give the end of the drill chance to wander before the cut is finished. The accurate hole that you already have acts as a guide for the next 'bite'. The other reason for using a brand new, accurately ground drill, is that it should drill dead to size. I have drilled holes this way and got the diameter accurate enough that there is a mild resistance to the reamer rotating. This kind of drilling takes time. Don't rush it by forcing the drill. That can also make the drill wander. Another reason for having a brand new drill.
It works for me, sot should work for you, as it is all down to the mechanics of the process. Give it a try.
Bob.
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Post by Roger on Mar 23, 2019 10:38:54 GMT
I missed reading this thread for a couple of days. I see there is quite a bit of talk about drilling deep holes accurately. This is how I drill a 3mm hole concentric to within 2 thou over a depth of the drill flutes, in the lathe, and it works with any size drill: First off I buy a brand new British made drill of the size I need. I say 'British' because I understand that the flute angles and corew diameters, of British drills differs from far eastern ones. Also I can be fairly certain of the quality. I use a No.1 centre drill to centre and don't drill so deep as to start the cone cutting. Just because the drill end is not perfect, doesn't matter. The fact that you are drilling into a rotating piece, automatically sets the drill cutting dead centre. That is why it has the name 'Dead Centre'. From this, you might say that if this was true then it should also be true for using a normal drill straight into the workpiece. It doesn't work like that because the length of the drill allows it to wander across the surface BEFORE it actually starts to cut, and if it digs in anywhere other than the dead centre, it will keep cutting from that point.. As long as you have a perfectly centred hole to start with, you can drill deep holes with almost no wander. The problems would start if the subsequent drill is not ground dead accurate so that the cutting edges are not cutting equal amounts and thus having equal forces acting on them. That's why I would use a brand new drill. Feed the final size drill in slowly, to just start the cut. Back off and take another cut for about 10 thou, back off sand then take another 10 thou cut. Keep taking these small 'bites' with the drill. Make sure there is no build-up of swarfe in the drill flutes, though this is unlikely with such short drilling 'bites'. You should be able to take the drill down to full flute depth and still have a hole that has not wandered more than about a couple of thou. I've done this numerous times with total success, clocked with a piece of silver steel in the resultant hole. The trick is the very short drilling cuts and the new drill. The reasoning behind this is that a: the new drill should be ground dead accurate, and b: the short 'bites' with the drill don't give the end of the drill chance to wander before the cut is finished. The accurate hole that you already have acts as a guide for the next 'bite'. The other reason for using a brand new, accurately ground drill, is that it should drill dead to size. I have drilled holes this way and got the diameter accurate enough that there is a mild resistance to the reamer rotating. This kind of drilling takes time. Don't rush it by forcing the drill. That can also make the drill wander. Another reason for having a brand new drill. It works for me, sot should work for you, as it is all down to the mechanics of the process. Give it a try. Bob. Hi Bob, I'd certainly agree with that, although Chinese made PCB drills are probably better ground than any HSS jobber drill, regardless of where it was made. Although what you say about the centre drilling is true, that doesn't follow with the flexible drill that you use afterwards. This is why I'm strongly making the point about holding the drill true to the axis of rotation. If you prepare to drill the job as you normally would, but instead put a clock on the chuck and clock around the drill, I think you'd be horrified at how far out it is. I've just done this test on my lathe, and although it's got a TIR of 60microns (2 thou) front to back, the TIR on the height is slightly beyond the range of the clock which is 0.2mm! In other words, the tailstock is over 0.1mm too high. This isn't important for most purposes, but I think it's an issue for the sort of job we're discussing and needs attention. Taking the argument to the extreme, picture attempting to drill the hole with the tailstock 1mm out of position. You can picture the drill being forced to start at the middle and then it would waggle around and head off towards the region opposite to the offset in the tailstock. My suggestion is that's what will happen with a small offset, albeit on a smaller scale.
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Post by 92220 on Mar 23, 2019 12:01:01 GMT
Hi Roger.
I agree with you on that. But for deeper holes, do they make PCB drills 40mm long? If they do, then I am in full agreement with you, but I've not come across any yet. All I can say is that I can drill a deep hole within a couple of thou of true, every time, using HSS drills. Yes you need to have a reasonably true tailstock, but if you use a flexible HSS drill after centring, and use the method I described, you should be able to get a hole 40mm deep, within 0.002" T.I.R., as long as the tailstock isn't massively out. I have no idea how close to 'true' mine is, because I built my lathe up from lots of secondhand parts bought from RDG Tools, when they still sold secondhand machines and parts, as well as off Ebay. For one job I used a 5/16" drill, to drill a hole that was 2.1/2" deep and the piece of silversteel I used to test it, ran true within 3 thou T.I.R. Yes you could get it even closer by clocking the chuck, as you suggest, but it is rare for a model engineer to need that sort of accuracy.
The reason my method works is that the true centre of a rotating mass is 'stationary' compared with the rest of it and a drill that doesn't flex, like a centre drill, will naturally find the Dead Centre, as long as the cutting point is not too large, hence my use of a No1 centre drill regardless of the final size. I use a PCB drill as a centre drill, when I want to drill deep small diameter holes.
I do agree that if you start off with a larger drill it won't follow this reasoning. If I want a large diameter hole I start with the No1 centre drill and then drill subsequent larger diameter holes until I get to the final size. As long as the cutting edge is not cutting more than 0.5mm it will drill concentric because the cutting forces are equal diametrically opposite, as long as both flutes cut equally.
When I want an accurate hole, I know I can get one every time. I have had holes that I have drilled an inch deep through, and when I have reversed the piece in the Griptru, when I have put my piece of silver steel in it and clocked it. the clock has not moved even one division, and it's a 0.0005" clock. It just works for me, so I would expect it to for anyone. Maybe my reasoning is wrong, but it works.
Bob.
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Post by Roger on Mar 23, 2019 12:49:19 GMT
Hi Roger. I agree with you on that. But for deeper holes, do they make PCB drills 40mm long? If they do, then I am in full agreement with you, but I've not come across any yet. All I can say is that I can drill a deep hole within a couple of thou of true, every time, using HSS drills. Yes you need to have a reasonably true tailstock, but if you use a flexible HSS drill after centring, and use the method I described, you should be able to get a hole 40mm deep, within 0.002" T.I.R., as long as the tailstock isn't massively out. I have no idea how close to 'true' mine is, because I built my lathe up from lots of secondhand parts bought from RDG Tools, when they still sold secondhand machines and parts, as well as off Ebay. For one job I used a 5/16" drill, to drill a hole that was 2.1/2" deep and the piece of silversteel I used to test it, ran true within 3 thou T.I.R. Yes you could get it even closer by clocking the chuck, as you suggest, but it is rare for a model engineer to need that sort of accuracy. The reason my method works is that the true centre of a rotating mass is 'stationary' compared with the rest of it and a drill that doesn't flex, like a centre drill, will naturally find the Dead Centre, as long as the cutting point is not too large, hence my use of a No1 centre drill regardless of the final size. I use a PCB drill as a centre drill, when I want to drill deep small diameter holes. I do agree that if you start off with a larger drill it won't follow this reasoning. If I want a large diameter hole I start with the No1 centre drill and then drill subsequent larger diameter holes until I get to the final size. As long as the cutting edge is not cutting more than 0.5mm it will drill concentric because the cutting forces are equal diametrically opposite, as long as both flutes cut equally. When I want an accurate hole, I know I can get one every time. I have had holes that I have drilled an inch deep through, and when I have reversed the piece in the Griptru, when I have put my piece of silver steel in it and clocked it. the clock has not moved even one division, and it's a 0.0005" clock. It just works for me, so I would expect it to for anyone. Maybe my reasoning is wrong, but it works. Bob. Hi Bob, PCB drills are limited to 10mm flute length which is all you're going to need for injector cones. Looking at what's been gleaned so far about accuracy, I wouldn't be confident that a couple of thou wander is good enough. That represents a significant proportion of the throat diameter in small injectors. I don't doubt that the method you describe gives good results though, I'm just trying to tease out what factors come into play when we're trying to split hairs. Agreed that a rigid centre drill will create a diameter that's true to the axis, although it's uncertain what the geometry inside the diameter where the tip of the drill makes contact looks like. Out of interest, runout is a huge issue in PCB drilling because the holes are so small and you're drilling them so quickly. Any runout causes huge eccentric loads on the spindle too, enough to seize the Air Bearing spindle. If you saw a machine drilling, you'd swear it was punching the holes, they're drilled that quickly. If the entry isn't absolutely central, the drill veers off to one side, describing an arc as it passes through the work. The only way to avoid this is to have a drill that's exquisitely sharpened centrally to the shank and the collet in the spindle has a runout in the order of a few microns. This is a very tall order considering the potential for runout issues in the spindle itself. This is precision engineering of the highest quality and I'm amazed they can make a 250,000RPM spindle and drill bit that meets these requirements and can drill three 0.2mm holes per second 1mm deep. These drills are made in their millions and it's why we can buy them so cheaply and know that the shank is going to have zero runout compared to the drill tip for all practical purposes. Most of these drills are made in China, and many of the Spindles are now too. It's worth remembering this when people claim that Chinese made items are of poor quality.... many of them are not.
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Post by suctionhose on Mar 23, 2019 22:33:36 GMT
To size the throat of a cone and be certain it is concentric with the reamed taper you make a parallel stub on the front of the d bit reamer.
as you turn up the blank for the reamer and before half dia is cut away the parallel stub can be mic'd and made exactly to the reqd throat size.
One of the published books - Brown or Lawrence - says to do this. I redesigned some steam cones once to get better range in injectors I had bought. I followed this method to remove the responsibilty of drills to be central, round and on size.
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jma1009
Elder Statesman
Posts: 5,896
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Post by jma1009 on Mar 24, 2019 0:21:46 GMT
Hi Ross,
This was the Laurie Lawrence method, which I always considered faulty. Not the way to proceed IMHO.
There are better methods, but we are getting off topic as to how design them, as to how to then make them.
How to drill everything to my mind comes under how to make them, as opposed to how to design them.
Laurie Lawrence described in ME twice (in the 1970s and the 1980s) how he did the steam cones and he must have had some very badly made (by him) taper reamers to come up with such a dogs dinner of a method. He also copied the commercial 'medium' 'standard' design of Arthur Grimmett/Ted Linden with no acknowledgement whatsoever. They were all SMEE members and ex-London. Arthur had broad shoulders and had by the publication in ME of the 1980s articles of Laurie Lawrence retired and was in his mid 70s. I recall a few low sonorous mutterings typical of Arthur in respect of Laurie Lawrence.
Other workshop 'chatter' from those who also knew Laurie Lawrence was far less complementary!
Cheers,
Julian
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Post by suctionhose on Mar 24, 2019 19:59:38 GMT
Fair comment Julian. In whatever way LL obtained the information he published it has been the basis for thousands of good injectors in these parts!
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robmort
Hi-poster
3.5" Duchess, finishing 2.5" gauge A3 and building 3.5" King
Posts: 172
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Post by robmort on Mar 24, 2019 20:32:05 GMT
...............Taking the argument to the extreme, picture attempting to drill the hole with the tailstock 1mm out of position. You can picture the drill being forced to start at the middle and then it would waggle around and head off towards the region opposite to the offset in the tailstock. My suggestion is that's what will happen with a small offset, albeit on a smaller scale. This seems to be a commom misconception. If the drill did "head off towards the region opposite to the offset in the tailstock", it would desribe a cone in the material being drilled, centred on the axis of rotation, and not an off-axis hole. When the job is rotating there is a self-centring effect, which does not apply when the drill is rotating and the job is fixed. The reason for off-axis holes is more to do with instabilities in the process which have never been explained fully to my knowledge.
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Post by Roger on Mar 24, 2019 21:58:25 GMT
...............Taking the argument to the extreme, picture attempting to drill the hole with the tailstock 1mm out of position. You can picture the drill being forced to start at the middle and then it would waggle around and head off towards the region opposite to the offset in the tailstock. My suggestion is that's what will happen with a small offset, albeit on a smaller scale. This seems to be a commom misconception. If the drill did "head off towards the region opposite to the offset in the tailstock", it would desribe a cone in the material being drilled, centred on the axis of rotation, and not an off-axis hole. When the job is rotating there is a self-centring effect, which does not apply when the drill is rotating and the job is fixed. The reason for off-axis holes is more to do with instabilities in the process which have never been explained fully to my knowledge. I don't think that's right. The drill would only describe a cone if it was rigid enough to resist the forces on it. In reality, once it heads away from the centre, the tip will be carried around in a circular motion. If that wasn't true, you would see all holes running perfectly down the axis of rotation, and we know that's not what happens. Once the drill heads off centre, it just keeps on going. I might just set the tailstock a mile off centre to see what actually happens. Watch this space!
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jma1009
Elder Statesman
Posts: 5,896
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Post by jma1009 on Mar 24, 2019 22:12:32 GMT
Fair comment Julian. In whatever way LL obtained the information he published it has been the basis for thousands of good injectors in these parts! Hi Ross, Yes, I agree the Laurie Lawrence published design of his 'standard' is a very good design, and not surprising as it was a copy of 2 proven commercial designs! Cheers, Julian
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Post by 92220 on Mar 25, 2019 8:58:46 GMT
Drills can do some really weird things! This was not done on a lathe, it was done on a hand fed pillar drill, but shows what drills can do. When I was an apprentice, I once saw a photo of a section through a block of steel that had been drilled with an extra long 3/16" dia drill. I think the drill was about 12" long, from memory. The hole started in the end but the drill curved itself during drilling and came out at one side of the block!! It was a well known photo in engineering circles, in those days. I will see if it has ever got onto the 'net.
Bob.
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Post by Roger on Mar 27, 2019 8:29:10 GMT
Ok, here's a thought I've been grappling with.... is there a reason why an injector won't work if you move the usual non-return valve to the outlet of the overflow? In other words, make the body exactly as it's done now, but leave out the ball and put a new non-return valve on the outlet.
We know that the injector can still work with the usual ball removed, you can look down and see the column of water. Obviously it's there to stop air being drawn into the Mixing cone and it won't work properly unless there's a solid column of water coming from the Mixing cone.
We also know that air is being drawn into the Delivery cone, hence some injectors, notably for Steel Boilers, have an additional non-return valve on the outlet.
So it begs the question, why won't it work with just that one? You obviously need the gap in the combining cone to allow the injector to create a vacuum and allow the excess air, water and steam to escape while starting. You need to prevent air from being sucked in there once it's started. However, that air has to come from the overflow, so why not stop it there instead of further in the injector?
I can see why it might be done the usual way for practical reasons. It's a convenient place to put the valve, in an upright position and it's a compact solution. However, on a scale GWR body, that's not the case. There's a parallel section where that valve would be. However, there is a valve on the outlet which could be made to work in a miniature injector.
Can anyone shed any light on this? Has it been tried before?
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Post by delaplume on Mar 27, 2019 10:58:15 GMT
Hi Roger,
Sorry--- can't answer that question but it's good to see "Outside - the - Box" thinking in operation......for which you have become rightfully well-known........Keep it up, matey !!!!
Best regards
Alan
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Post by suctionhose on Mar 28, 2019 20:03:58 GMT
Roger, I suspect the reason most model injectors are configured in the same way is 'Gravity'. A ball that naturally seats and an overflow that naturally drains... Full size injectors come in many configurations - one marvels at the engineers behind them - but for the bare essentials for reliable model usage, they are what they've become. The function of the ball is to help automatic restarting by destroying the vacuum, equalizing pressures between chambers and allowing the energy exchange to start over. A fellow at our club who has made many injectors to the LL words and music, made one with no ball. It worked well except for needing help to restart if it knocked off. I remember meeting Charles Dockstader at his club in LA in 1985. His loco had a miniature injector in the cab up on the boiler with the lever and moving steam cone... twas perfect in every sense! I'm just saying other combinations are possible and people do experiment a bit. Depends on the individuals motives. In the context of a whole working model, the injector is just one small piece. I couldn't justify spending a year or two inventing a new way (although I may make a scale body injector for my 1880 TE using Brown's cartridge method)
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JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,902
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Post by JonL on Mar 28, 2019 20:13:18 GMT
This mention of restarting injectors if they knock off and other items, I'll be honest I don't actually know how to operate one. Am I right in saying: 1. Open water valve 2. Open steam valve quite far to get it going 3. Throttle back the steam valve to the rate you want 4. if it stops close the steam valve all the way then go to step 2?
Excuse my ignorance.
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Post by Roger on Mar 28, 2019 21:21:47 GMT
Roger, I suspect the reason most model injectors are configured in the same way is 'Gravity'. A ball that naturally seats and an overflow that naturally drains... Full size injectors come in many configurations - one marvels at the engineers behind them - but for the bare essentials for reliable model usage, they are what they've become. The function of the ball is to help automatic restarting by destroying the vacuum, equalizing pressures between chambers and allowing the energy exchange to start over. A fellow at our club who has made many injectors to the LL words and music, made one with no ball. It worked well except for needing help to restart if it knocked off. I remember meeting Charles Dockstader at his club in LA in 1985. His loco had a miniature injector in the cab up on the boiler with the lever and moving steam cone... twas perfect in every sense! I'm just saying other combinations are possible and people do experiment a bit. Depends on the individuals motives. In the context of a whole working model, the injector is just one small piece. I couldn't justify spending a year or two inventing a new way (although I may make a scale body injector for my 1880 TE using Brown's cartridge method) Hi Ross, I was coming to the same conclusion, ie that gravity and a convenient layout were probably the reasons for them being how they are. I'm not sure that's the right explanation for the ball valve though. My understanding is that it would restart without a ball, but may not continue delivery because of the air drawn in from the gap in the combining cone. Hopefully a few experiments will discover what you can and can't do. I'm hoping to work quickly through the injector design, after all, most of the hard work has already been done, ie the cone throat dimensions, angles and gaps. I find this sort of thing fascinating, so I don't mind spending a bit of time figuring it out for myself.
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Post by Roger on Mar 28, 2019 21:28:26 GMT
This mention of restarting injectors if they knock off and other items, I'll be honest I don't actually know how to operate one. Am I right in saying: 1. Open water valve 2. Open steam valve quite far to get it going 3. Throttle back the steam valve to the rate you want 4. if it stops close the steam valve all the way then go to step 2? Excuse my ignorance. Yes, open the water valve first, there's no point in having steam if there's no water to be fed into the boiler. It would also just serve to heat up the injector body which is something you want to avoid. Once on, the steam can usually be turned on wide, but you might have to close the water valve a little to make it pick up if the regulation isn't quite right. There's a gap between the Steam cone and the Condensing cone that serves to limit the amount of water that can be drawn in. If that's too large I understand that it will pick up too much water and won't want to start. The rate isn't regulated by the steam valve, it's either delivering or it isn't. Generally speaking, it shouldn't stop until you close the steam valve. It should restart on its own even if it stops for some reason.
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