simon hudson Posted September 10, 2012 Share Posted September 10, 2012 I have eventually started building my Gibson 01 chassis and have reached the point of making coupling rods.I have had a couple of disastorous attempts.I have read and re-read Mr Rices excellent book, and had some good advice from Markits wheels. I'm using Markits fine crank pins and bushes.My problem Mr Rice states emphatically"Do not use a drill or a needle file" to open up coupling rod holes use a "taper broach". Question 1) Is there a difference between a cutting broach and a taper broach-I cant get my head around not using a drill or needle file surley any hand tool is liable to go off centre Question 2) How to use a broach-Going back to my schooldays 40 yrs ago I thought a broach was similar to a rasp!! OK I have googled broach so I'm a little enlightend. I have used the search function and drawn a blank I hope the questions aren't daft or silly my philosophy is if you don't ask you wont find out Link to post Share on other sites More sharing options...
Miss Prism Posted September 10, 2012 Share Posted September 10, 2012 All broaches are 5-sided tapered things. They come in two varieties: cutting broaches (with sharp edges) and smoothing broaches (without sharp edges). What is needed to 'open up' an etched coupling rod hole depends on the state of the etch and how much opening up is needed. There is a danger if using a drill in thin etched metal that it will 'snatch' on the half-etch and wander off-centre. A cutting broach is therefore more controllable. If the drill is in a proper vertical stand and can be controlled, and the rods are clamped firmly on the standbed, undersize drilling is a useful means of putting parallel bores through both rod sets, following which they can be broached out to however close a crankpin bush fit you want. Smoothing broaches will not cut, and will only harden and polish. There is little use for them in normal 4mm scale. Link to post Share on other sites More sharing options...
Coombe Barton Posted September 10, 2012 Share Posted September 10, 2012 Something like these http://www.chronos.ltd.uk/acatalog/Modelcraft_Broach_Sets_.html Link to post Share on other sites More sharing options...
trisonic Posted September 10, 2012 Share Posted September 10, 2012 Broaches are not necessarily tapered. My friend in the UK owned an Industrial Engineering company that made the broaches for Ford to ensure that their engine blocks and heads were perfectly flat (where they met). Best, Pete. Link to post Share on other sites More sharing options...
Miss Prism Posted September 10, 2012 Share Posted September 10, 2012 Broaches are not necessarily tapered. My friend in the UK owned an Industrial Engineering company that made the broaches for Ford to ensure that their engine blocks and heads were perfectly flat (where they met). I think that is what is called a 'special'... Link to post Share on other sites More sharing options...
trisonic Posted September 10, 2012 Share Posted September 10, 2012 I think that is what is called a 'special'... Dunno. He bought a Ferrari from that deal, though.... Best, Pete. Link to post Share on other sites More sharing options...
Coombe Barton Posted September 10, 2012 Share Posted September 10, 2012 I used to ream out engine blocks with a file and then bang the copper tubes in with a mallet and ream them with the end of a Jemmy to make em fit...... there may have been some Loctite 601 (602?) involved too........ Not P4 techniques, then. Link to post Share on other sites More sharing options...
simon hudson Posted September 10, 2012 Author Share Posted September 10, 2012 Already checked the link Thanks Coombe Barton also checked out some watch/clockmakers broaches.I was tempted, but held off until I'd posted my queries. Re the rods I'm doing, Gibson do the frames but not matching rods!!? so I'm using their universal rods.I tried using dividers as per Mr Rice I actually got the measurements spot on, but ballsed the rods up with oversize and oval holes!! so I have purchased a set of Jig axles and got some very good advice from Mr Markits ( a very helpful gentleman) I think I might take a punt on some broaches. I haven't started a build thread in the relevant topic because I don't yet feel confident enough to attempt it but I have assembled a HighLevel load hauler gear box assembly with motor I have got the chassis up to brake gear etc I just need to sort these rods out.Thanks for the help as usual this forum is a great place to learn Link to post Share on other sites More sharing options...
halfwit Posted September 10, 2012 Share Posted September 10, 2012 With a broach you can open out a hole by a thou. or so, usefull when coupling rods have a slight bind. Also usefull for opening out etched holes for handrails etc. Every etched kit builder should have a set. Link to post Share on other sites More sharing options...
Coombe Barton Posted September 10, 2012 Share Posted September 10, 2012 I haven't started a build thread in the relevant topic because I don't yet feel confident enough to attempt it but I have assembled a HighLevel load hauler gear box assembly with motor I have got the chassis up to brake gear etc I just need to sort these rods out. When using broaches the operative words are slow and gentle. Do a bit. Check. Do a bit more. Check again. Do a bit more, check again And so on. The difference between fitting and sloppy is very small. Giving it a bit of wellie will be counter productive. (Don't ask how I know.) And make sure your work is well supported - as with drills cutting broaches can bind and you'll bend things. Even smoothing broaches can bind, so be aware that once you start employing friction it can turn against you. Link to post Share on other sites More sharing options...
Horsetan Posted September 10, 2012 Share Posted September 10, 2012 Not P4 techniques, then. Unless it was a Rover P4.... Link to post Share on other sites More sharing options...
RMweb Gold mcowgill Posted September 10, 2012 RMweb Gold Share Posted September 10, 2012 I used to ream out engine blocks with a file and then bang the copper tubes in with a mallet and ream them with the end of a Jemmy to make em fit...... there may have been some Loctite 601 (602?) involved too........ I've always wondered how Longbridge fitted the cylinder liners to my MG TF engine with such accuracy.... Link to post Share on other sites More sharing options...
edcayton Posted September 11, 2012 Share Posted September 11, 2012 I may be thinking of a different thing here, but all broaches I have ever come across have produced parallel shapes, albeit some complex ones, by pushing or pulling a series of cutting tools across the job with each tooth taking a bit more material. The broach itself looks tapered due to the teeth becoming progressively larger. For shallow tapers in round holes I have always used a taper REAMER, which can open up a previously drilled hole of the correct size. Ed Link to post Share on other sites More sharing options...
Blacque Jacque Posted September 11, 2012 Share Posted September 11, 2012 I too use taper pin reamers. Generally they have 4 flutes. They can snatch in thin material if you're not careful, but this is true of any cutting tool. The item linked above, whilst described as a broach, is actually much more like a taper pin reamer. Indeed the action referred to is a reaming operation. Strictly speaking a broach has multiple teeth & is not a fluted tool. Link to post Share on other sites More sharing options...
Arthur Posted September 11, 2012 Share Posted September 11, 2012 That's clarified it. I couldn't understand how the broach being discussed earlier to open out holes, an operation I'm familiar with, could also have been used to machine mating flat surfaces. Wrong names. So, a taper reamer to open out holes and a broach, which apparently comes in many forms, to machine flats, slots, keyways etc. Thanks for that. Should you be interested; http://en.wikipedia.org/wiki/Broaching_(metalworking) Link to post Share on other sites More sharing options...
Blacque Jacque Posted September 11, 2012 Share Posted September 11, 2012 Just for reference, true taper pin reamers have a strictly defined taper of 1:48 for imperial pins & 1:50 for metric. Link to post Share on other sites More sharing options...
Kenton Posted September 11, 2012 Share Posted September 11, 2012 Every etched kit builder should have a set. Absolutely. And if you build many kits a wide range of them. I don't think I have ever build a chassis without using them and agree totally with Ricey that drilling a hole is a totally different engineering bodge (especially if done by hand). 5 sided tapered broaches do come in sets and it is worth buying a good set (Eileens and others sell suitable ones) These are cutting broaches and should not be confused with reamers which are a different tool. Yes, you can get a set of straight edge/parallel broaches (these are the ones referred to as smooth or finishing and are useful for precise holes - they are rarely used except with thicker metal. A taper broach will cut a cone shaped hole that inevitably is oversize on the outer side of the cone. Think of an axle bearing hole in this form and you will see that the axle bearing will only be supported at the smaller end of the cone so the bearing to frame join will be a weak spot. Though most folk swamp the hole with solder! Always start a hole small - probably half diameter drilled and then use a progressive size broach to 'cut' the hole out to the size required. They should be hand finger twisted slowly and you should never attempt to force the turn or use them in the chuck of a power tool. It is very easy to damage them and remember that any working of metal will harden it. If it is very thick metal (eg.chassis frame) the application of a little heat to the hole (eg. from a gas soldering burner) can soften the metal and enable easy cutting to continue. Oh and try to use the centre of the broach's length the cutting ability is best at this point, at the pointy end they tend to cut too quickly and it is easy to over cut. At the other handle end there is too much gap between the cutting edges and it is easy to take the hole out of true round by angling the broach. As for round files - ditch them - their only use is for making oval holes - useless for engineering tasks. Link to post Share on other sites More sharing options...
Blacque Jacque Posted September 11, 2012 Share Posted September 11, 2012 This is true of any cutting tool when used incorrectly, the 5 sided broaches being discussed here will cut a wobbly hexagonal hole if not used with care. Link to post Share on other sites More sharing options...
simon hudson Posted September 11, 2012 Author Share Posted September 11, 2012 Broaches ordered so a little time to get on with the superstructure thanks for advice I feel a lot happier and will put some photos up later Link to post Share on other sites More sharing options...
laurenceb Posted September 12, 2012 Share Posted September 12, 2012 I too use taper pin reamers. Generally they have 4 flutes. They can snatch in thin material if you're not careful, but this is true of any cutting tool. The item linked above, whilst described as a broach, is actually much more like a taper pin reamer. Indeed the action referred to is a reaming operation. Strictly speaking a broach has multiple teeth & is not a fluted tool. ]There are 2 diferent kinds of cutting tool called a broach an engineering and a watchmakers. The kind used in model making is the watch makers the engineers broach is pushed through the material to make non round holes such as those in Romford or Slaters wheels Lauernce Link to post Share on other sites More sharing options...
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