Member postings for mick

If we're talking about holding work in a three jaw chuck, then shim is okay, but will not hold the job true and potentially the job could pull out of the chuck. A four jaw self centering chuck is the best chuck for every day turning, as the jaws have a very small surface clamping area where the clamping pressure is more evenly distributed across the four jaws, with the result of firmly clamping the work piece, while not marking the surface, even previously finish turned ones. The only time I use a three jaw chuck is to hold a hexagon.

Thanks to all. A kilo of Polybend has been ordered.

Sorry for any confusion, typo error, wall thickness is: 0.025''. Ordinary tube benders will undoubtedly crush the section, filling the tube with sand or salt is an option, but the grains can migrate while bending leaving the bend unsupported, pipe tubes and springs are okay for ductile pipe, such as copper. There needs to be a solid but ductile medium inside the tube to support the bend while its being formed, as I'm not running to a set of hydraulic benders which would most probably stand more chance of generating the bends without crushing. I'll try the water and detergent when the time comes and report back.

I've got to bend a quantity of 5/16'' dia. x 0.25'' thick walled brass tube to form inlet and exhausts pipes, now I know all about annealing prior to forming, but of course the risk of the section collapsing is ever present. I've read about filling the tube with molten solder, or foundry metal, but I've just read a piece about freezing a mixture of water and detergent inside the tube and then forming the bends. Has anyone tried this method?

You haven't said which grade of MS your using, which could be the root of the problem, either that or a reamer that's seen better days

Leaving 0.3 on the bore is okay all the time the drilled hole is smooth, as the ruff surface finish could be what's left from the drilling operation. To achieve a smooth drilled hole double drill, that is, drill the pilot hole at 15mm and follow up with the 15.7, this will give you a size, smooth bore. Always use factory ground drills for this operation

I call myself a modest hero and a friend of the people, but I still don't need another selection box of roll pins!!!

Brilliant, thanks Jason. I've already got a selection box of roll pins and didn't really need another one just to get the couple a needed.

Thanks again.

I love the internet, but there are times when trying to find a supplier for want you need can be very frustrating. Just spend a while trying to source 1/16'' x 5/8'' ( I could take longer and cut them down) slotted spring pins aka roll pins.

There are firms that will supply, but in boxes of 200, or firms who will make them to order, but none that do smaller quantities. In the past someone has always come up with a supplier for what ever I was trying to source at the time, I hope this will be no exception.

Thanks

Well Adam, the only inserted tools I use on a regular basis on my Myford are a couple of Glaze right and left hand profiling tool holders and a rear mounted parting blade. I have a couple of screw cutting tool holders on a 20mm squ. body, which, when mounted on a couple of 5/16'' strips directly to the compound slide base gives centre height. The rest of the industrial tool holders I have acquired over a working lifetime remain in the tool chest.

I've dipped my toes in this murky water before. To my mind Its probably best to buy inserted tooling from a supplier that advertises to the model engineering fatuity, as the grade of carbide and tool shape they supply will be a happy half way house that will preform well in a variety of different applications.

To try and get industrial style inserted tooling to work in a hobby environment is only at best a get out of jail option.

When I worked in industry I use to favor the double side triangular style of tool holder, but had different inserts for just about every material I machined on a regular basis. If the inserts were placed side by side its virtually impossible to see the difference between, but difference there is when machining, a stainless steel insert will preform poorly when cutting cast iron and visa versa, cast iron inserts preform badly when cutting anything but cast iron.

The point I was trying to make regarding the unsuitability of files to make spade drills, has nothing to do with annealing the file before attempting the manufacture. The file, with its thin and wide section is completely wrong for this application, because as soon as the drill started to bite into metal the torque would snap it like a carrot.

Back in the day spade drills were forged from round carbon steel bar, so giving them the molecular structure needed to withstand the torque pressures and providing a round shank with which to hold it in the drill.

The photo's are from an old workshop text book I have in my collection, which also goes to underline my point about missing digets.

When I was a lad a lot of the old boys had various fingers missing, I suspect as a direct result of what you are proposing to do. Spade drills are dangerous things, especially if not completely concentric and should only be used in a industrial machine tool. Files are carbon steel and therefore prone to shattering if not used for their intended purpose of being pushed backward and forward. The "D" bit approach would be, in my opinion, the preferred option.

The problem, as I see it, is that in these days of inserted and pre-ground tooling and charts of cutting speeds and feeds for each style of tooling, everyone expects to achieve a good finish because they have bought the tool for the job, so it should deliver. Back when the world was very young things were completely different, with hand ground HSS every job was different, in fact, after rough turning to 0.020'' over size, a turner would experiment with different speeds and feeds before committing to the finial cut to size, as the same machining conditions couldn't be guaranteed from one work piece to another. Taking onboard all of Andrew's points, I feel its good practice to try different approaches, but for finishing, the general rule of thumb is dead sharp tooling, light depth of cut, experiment with speeds and feeds and use plenty of soluble oil, cutting oil or paste applied with a brush brush if no machine fed coolant is available. To become an all round machinist it was expected to take a five year apprenticeship, so you have only just taken the first steps, but good luck with it all.

If you have a milling machine, rest the cylinder in the bed tennon and fix some sort of scriber in a drill chuck or collet and simply move the table along marking the outside as you go.

Nobby has it just about right, back when the world was young they were used mainly on mould and die tools, to file a local area without touching any of the surrounding metal. They come in a wide range of blade shapes and profiles, which allow the cutting face to be cantered over to reach awkward internal areas. I still have a good selection, which I now find useful to clean stubborn machining marks around CNC generated islands.

I don't doubt that a lot of machinists regularly trepan out large diameter holes, all I'm suggesting is, if you haven't attempted it before a half inch thick piece of MS plate is not exactly the best place to start.

Taking on board all of the above, which, in the case of trepanning, require special skills, or buying a hole saw,in the long run it would be just as easy to drill, using your largest diameter and face out from that initial hole, it shouldn't take that long.

If you have any die head chasers they are great for cutting multi start threads. Just grind them back to two teeth for a double start, three for a treble etc and set the gear box/change gears to two or three times the pitch and screw cut. Avoids any problems that can occur cutting the thread two or three times by advancing the compound slide.

If the pin were parallel then there would have to be a working tolerance between the two, which would mean there would be movement between the two. A taper pin allows the clapper box to move without any movement against the pin. Over the years a degree of wear may occur between the hardened pin and the cast iron clapper box, in which case the two parts, the clapper box and the tool slide should be visited with a taper reamer to re-instate a continuous fit before fitting a new pin.