Member postings for Andrew Johnston

Both.

Andrew

In the UK a 10mm HSS TiN 4-facet drill is around £6. Most of the replacement drills I buy are less than 6mm, so a pound or two. I run my drills fairly hard so they are normally beyond a simple resharpen when replaced.

If I really need to resharpen a drill then I can do it by hand, or use the Clarkson T&C cutter grinder and drill and tap accessory.

Andrew

Busy day today! The usual Spitfires flying over, but an hour ago the Catalina rumbled past the bungalow at about a 1000ft. Shortly afterwards, as i was about to start cutting the front grass, the Lancaster flew over at 600ft, heading for Duxford.

Andrew

Being truly lazy I just buy new drills, at least in small sizes, say less than 1/2".

Andrew

The screw is there to stop the collet turning when the drawbar is tightened. Get rid of it and see if that makes any difference. Neither of my R8 mills have the screw fitted.

Andrew

Wrong product; they're designed to lift vehicles without damaging them. Any damping will be coincidental.

The lathe shouldn't be producing significant vibration so I am not sure why there is a need to isolate it from a concrete floor?

Andrew

Neat cutting oils are intended to lubricate, not cool. So they tend to get used for high pressure cutting applications such as gear shaping. Soluble oils provide cooling (due to the water) but not much lubrication. I use soluble oils when machining, but only with HSS tooling. Both brass and aluminium are turned dry. Personally I'd bin the cutting oil and turn dry to start with.

I have never worn a mask in the workshop and have never felt the need to do so. Neither do I have an extractor fan. The garage door isn't a close fit and that seems to be sufficient for air circulation.

Andrew

I agree with Howard; I've just cleaned up a 2mm pitch thread in Delrin that had been crossthreaded for a friend. Only too easy to get it crossthreaded. So a finer thread in a soft plastic will be a nightmare.

Additionally PTFE is horrid to machine when trying to hold tolerances. It is soft and creeps rather than cuts. Cut, measure to size, and the next morining it will have moved.

Use the coarsest thread possible and ideally use glass filled PTFE. It is much more stable when machining.

Andrew

Fortunately there is one less now.

Andrew

I'm neutral on the subject of ball turners; I don't have one, and don't need one.

I was intrigued by Vic's powered ball turner. I wonder if it can do concave curves? And if so could it be adapted to cut a double enveloping worm?

Andrew

He prefaces it by saying that it is false economy buying a secondhand lathe. There's a difference between worn and misaligned. Worn ways can be compensated for by various means. A misaligned headstock would be very difficult to deal with, to the extent that one would be essentially using the lathe simply as turns. Assuming a quality watchmaking lathe in the first place it is highly unlikely that the headstock would become misaligned, unless maltreated such as being dropped.

Andrew

Would that include the hours spent creating CAD drawings, generating G-code and designing and making fixtures?

Andrew

Drawbars are essential for INT40 holders. The taper is self releasing (in theory) and so needs a positive means of retention. Drive is via dogs, not via friction on the tapered surfaces. The drawbar is simply to keep the holder in place, so strength is not an issue. All my INT40 tooling has a threaded parallel end; 5/8" BSW for older holders and M16 for newer holders. I think INT30 used 1/2" BSW.

As I understand it the Beaver mill came with INT30 as standard with an option for INT40. It seems strange that the quill bore is only 14mm. Either Beaver used custom INT40 holders to force the customer to buy from them. Or the conversion to INT40 isn't an original factory fit.

Andrew

All of the smaller Coventry dieheads have hardened bodies.

Andrew

All of the smaller Coventry dieheads have hardened bodies.

Andrew

Technically sheet and plate are cold rolled. Sections such as round/hexagon/rectangular are cold drawn through a die. Hence the description BDMS, equals bright drawn mild steel. It is the distortion caused by drawing through a die to reduce the size that causes the surface stresses.

The issue occurs on any material that is cold drawn. In the past I have had serious bending problems when machining brass sections.

Andrew

Screw threads are far more complex than most people realise.

1. Manufacturers sell to commercial machine shops who have the knowledge to work it out. They are not interested in the tiny amateur market.

2. I use full form inserts, topslide parallel to the lathe axis, and a calculated depth of cut. Once done I check with mating part, if it doesn't fit take a couple of thou off the diameter and repeat as needed. For multiple parts once the initial thread is cut there is a number on the cross slide dial to hit, plus a sanity check that the mating part fits.

3. The full form inserts shape the crest and remove fine burrs produced by the screw cutting. Commercial screw threads are made to published tolerance grades all of which have ODs slightly less than nominal. I've just measured the OD of a commercial 1/4" BSF set screw, which is 0.245", ie, 5 thou under.

Professional machine shops use a similar trial and errror method, but they use precision ground go/nogo thread gauges for checking.

Andrew

Wrong!

As SoD says a full form insert will finish the crests of the thread and also have the correct profile for the root for the thread pitch to be cut. A partial insert has a very small radius for the root. For coarser threads in the range covered by the partial form insert the depth of cut will need to be increased over the theoretical value.

I use full form inserts; can't be ^^^^d to faff about with partial form inserts. In practice I find that the theoretical thread depths are fairly accurate. One might have to cut a thou or two deeper to get a nice fit. But there's nothing to say that the female thread is accurate.

Andrew

It's a machine reamer not a hand reamer. Unlike a hand reamer it has a 45 degree angle on the front and those are the cutting edges. The start of the flutes are not tapered like a hand reamer. It doesn't have a square on the shank because it doesn't need one. it will be held in a chuck on a machine tool.

Andrew

I was commenting on the description by Nealeb. Of course it is entirely possible that I have misunderstood the method.

Andrew