Member postings for Andrew Johnston

My thought entirely. Why not make the part from gauge plate? It's tougher than mild steel, and is easy to harden if needed.

Regards,

Andrew

Best we stick to the previously mentioned circular transcendental functions then - Andrew

Hmmmmm, I can't work out if I'm being agreed with, or insulted............

Andrew

PS: I am assuming that people understood the mathematical connotations in my original post.

I've been using 3D PDFs to send parts to clients for some years; so far I've never found a way to make measurements. The PDF files are smaller than the native part files by about an order of magnitude. I assume the PDFs define the part in a way that does not allow measurement?

Regards,

Andrew

Hi Raymond,

Probably the first thing to do is work out what you want/need to make. That will give you an idea of the size of machine and complexity of software required.

I have no knowledge of the Syil machine. However I have been running a Tormach PCNC1100 with 4th axis in my workshop for the last three years. Overall I have been very pleased with my machine. I've made hundreds of parts in plastics, aluminium, cast iron, gauge plate and stainless steel. The machine has always done what I asked. I have had a few minor issues, but Tormach's support has been excellent, fast response and quick delivery from the US if required. In terms of accuracy I'd say the Tormach wasn't far off the normal jobbing professional CNC workshop. I've made prototypes of complex heatsinks that have then been replicated by a professional CNC company and have had the opportunity to measure both - not much difference. We rejected the professionally made heatsinks because they weren't up to scratch (didn't follow my advice), but that's another story.

I have not used NX, but I'd urge caution, as others have already mentioned. I use a lot of high end CAD for work (Mentor Graphics/Cadence/ProEngineer) and while the programs are incredibly versatile they are also extremely expensive, difficult to learn, and probably overkill even for small companies. I use Alibre for 3D CAD and Visualmill for CAM. I'm not convinced that Visualmill was the correct choice, but I'm not planning to change at the moment. If I was looking again I'd seriously consider OneCNC for CAM.

I did write a couple of articles on the Tormach for MEW. a while back If you don't have access to them PM me and we'll see what we can arrange.

Regards,

Andrew

Sorted! Thanks one and all for the suggestions; they helped me clarify my thoughts and identify the problem. A special mention for Nigel, who, in essence, identified the actual issue.

A quick look at a number of previous turning exercises showed a very slight banding on stainless steel, but on nothing else as far as I could see. This tells us the problem is not specifically related to silver steel, but may be related to tougher materials, and hence higher cutting forces. My lathe is a Harrison M300, on the makers stand, and solidly bolted to a concrete floor. It is three phase and runs from a true three phase supply. The chuck is a Burnerd high speed collet chuck. Thus I discounted vibration from the machine itself, or the main motor. I calculated a few frequencies for spindle speed and the rough frequency of the banding, but no obvious resonances sprang to mind. I didn't do the calculations for the drive train, as the fine feeds are driven by a separate drive shaft rather than the leadscrew.

Now what I didn't tell you is that the cross slide is a fairly easy fit, and one of the bolts that holds the top slide down is a bit iffy. Yes, I know it's obvious in retrospect but us country boys are a bit slow on t'uptake.

The task this morning was to make and fit two new T-bolts for the top slide, like this:

As an aside I discovered that the cross slide tapered gib has a special brass insert and grub screw pressing on it from the side of the cross slide, as well as the normal adjustment screws each end. I never knew that! It's not mentiond in the manual either, although it is shown in the exploded parts drawing.

With everything cleaned, adjusted and re-assembled I tried another couple of tests on the original silver steel bar. Both tests were done at 1200rpm, 0.2mm radius insert, depth of cut 20 thou, and feedrate 2 thou/rev, one test with coolant, one without. In both cases the swarf came off as a long open spiral. Both surfaces look pretty uniform under the magnifying glass, with just a hint of tearing in places, although the finish doesn't feel rough. Surface roughness measurements (Ra, µm) are:

With coolant: 2.15 1.72 2.10 Average=1.99

Without coolant: 1.40 1.55 1.40 Average=1.45

So in this case without coolant seems better, which is what I would have originally expected.

As is so often the case the solution to what seems to be a mysterious effect is actually very simple, in this case operator stupidity. I should have fixed the iffy bolt issue long ago.

Regards,

Andrew

Quite so, it's got nothing to do with the earth's surface; the plane is being set perpendicular to the local gravity tensor.

Andrew

Here's my personal method, which may or may not be applicable depending on what equipment is available.

For precision parts I never mark out or centre pop hole locations. All holes are drilled straight off on the vertical mill using the DRO. I find that four facet drills start more accurately without a centre pop on any flat surface, machined or cold drawn. For surfaces that are not flat I either mill a flat first, or start with a carbide spot drill.

I only mark out and centre pop for sheet metal work where everything will be done by hand, or for DIY bodgery.

Regards,

Andrew

Good question; and the answer is......neither. Close examination with a magnifying glass shows that the banding is in fact a multi-start thread. I counted eight starts. That implies that the phenomenon that is causing the banding is to some extent regular in time, and at a rate about eight times the spindle speed. Whether it is actually locked to the spindle speed is another matter.

I did another couple of tests. One at 1700rpm with coolant; the banding is still there. It's difficult to tell if it is at a different spacing. I also tried a test at 1200rpm, with coolant, on a different bar, albeit from the same source. This also exhibited some banding, but much less obvious. You have to get the light on it at the correct angle to see the banding.

On the next test I'll dig out a piece of genuine Peter Stubs silver steel and try that.

Regards,

Andrew

Here is a picture of the results of another quick trial. The first 1/2", from the right, was run at 40 thou doc, 2 thou/rev, 1200rpm and no coolant. The remainder up to the first step is identical, except for coolant. The last step, on the left, was 20 thou doc, with coolant, the other parameters the same.

The finish with no coolant is torn under the magnifying glass, the other finishes are not torn, but there is a definite and regular difference in the finish, which shows up as the banding. Surface roughness measurements, from the right, are 3.15µm, 1.80µm and 2.16µm respectively. Certainly on the results from this quick test I'd use coolant on silver steel. All very confusing.

I guess the next thing to try is a different bar, from a different supplier.

Regards,

Andrew

I'm puzzled by the banding. I've never seen it before over a wide range of materials and tooling, both HSS and carbide. Mind you I almost never polish after turning; may be that's why I haven't seen it before. The leadscrew pitch on my lathe is 1/4", and the banding was roughly every 40 thou, so may be not the cause? The banding was a difference in colour, metallic and dark, rather than a mechanical feature, almost like staining. I can't see what is special about silver steel that should cause it to stain. Could be a heating/cooling effect I suppose, but coolant means flood coolant, not a dribble, so why does it appear at this particular repetition rate? Anybody got any other ideas?

If I get time this week I'll have another go and see if I can reproduce it. If so, I'll try and examine it in more detail.

Regards,

Andrew

After a bit of a break, I've done another set of trials; this time on silver steel. The silver steel used was 25mm diameter, recently bought in my local professional tool warehouse. There's no direct equivalent in Machinery's Handbook, but I think that the tool steel W1 is a fairly close match; W1 is a high carbon plain steel for water hardening. For W1 the recommended speeds are 100fpm for HSS and 350fpm for uncoated carbide. For these trials I used speeds of 370rpm and 1200rpm. The insert used was a 0.2mm radius insert from Korloy, grade NC3120 for steel. In view of the small nose radius in each case depth of cut was 20 thou and a feed rate of 2 thou/rev. I tried four combinations:

Edited By Andrew Johnston on 21/05/2012 21:59:44

Sorry John, you've been beaten to it. Romney Marsh has already been allocated as a nuclear waste dump......it was on the BBC recently, so it must be true.

I started off with my Bridgeport in a corner, but it soon got moved as I acquired more scrap iron; sorry valuable second user machine tools! It now sits along a wall, but canted about 20° from perpendicular. One problem having it in a corner, apart from workpiece length, is having the room to swing the ram, if you have heads on both ends. At each stage of my workshop planning I tried various locations using cut outs of the machine tools (reflecting maximum table travels) and a plan of the workshop on graph paper. Much quicker than moving the machines only to find they won't fit; although it does keep one fit, even if the machines don't.

Regards,

Andrew

If indeed it is a tension/compression tapping head then, yes, it is intended for use on a machine where the spindle can reverse quickly and automatically. In practise that means CNC. It would be possible to use one on a drill press, but I expect it would get tedious rather quickly, with a high probability of making a boo-boo in the sequernce of operations, well it would for me anyway. It would also be tricky to use on a manual machine for blind holes.

Regards,

Andrew

A quick search on the internet seems to show that this is a tension/compression tapping head, so yes, you will need to reverse the spindle in order to back the tap out.

I can't help with specific advice on using a drill press, as I've only ever used my tension/compression tapping head on a CNC mill where the whole operation is automatic and spindle reverse it pretty quick, less than two rotations.

Regards,

Andrew

Phil: Thanks for the elucidation. However, synchronous motors can be designed with varying numbers of poles to vary the speed, in a similar fashion to an induction motor. See for instance:

Although if you need to fine tune the speed then I agree that a VFD is required, in both cases.

Bruce: A question; is it an urban myth that the US doesn't have a national grid, in the same way as the UK? As far as I recall when there was a huge power outage on the US East coast some years ago the smug commentators on the BBC put it down to the 'fact' that the US electrical network wasn't a true grid.

Regards,

Andrew

Edited By Katy Purvis on 01/06/2015 12:27:45

Hmmmm, some confusion here methinks. A synchronous motor is just that, the rotation speed is synchronised to the frequency of the line voltage. A synchronous motor does not have slip, nor does it need slip to produce torque. In contrast an induction motor does need slip to produce torque, which is why an induction motor is classified as an asynchronous machine.

Regards,

Andrew

Doooh, I can't move it into the kitchen because:

1) There's no 3-phase in the kitchen

2) It'd take me ages to dismantle it, and even then I don't think I could lift the base

3) All my drills are in the workshop

4) The kitchen is already full, as illustrated here:

Regards,

Andrew

Swarf Mostly: Blimey, how the h*ll did you know that? And here's a picture:

I've never come across another drill like it, or even seen much about them on the web.

As one can see it's a bit enclosed, so in reality I can work with much larger workpieces on my vertical mill. I also spend quite a lot of time planning out jobs so I don't generally need to drill a hole urgently, while the mill is occupied with something else. Saves on scrap too!

Regards,

Andrew

Pailo: I'm with the minority on this one; if you are constrained on space and don't use the pillar drill, then move it on. Personally I hardly ever use mine, less than 0.1% of holes. But I'm not constrained by space, and it's rather an odd drill, so I hang on to it. The drill was almost certainly part of WWII 'lend-lease'. One of it's disadvantages is that the spindle has a built in Jacobs taper, so it's difficult to swap to other tools. I have several Tapmatic style units, but I've only ever used them on the vertical mill.

Now as to the important question of where to put ones tea I agree with Steve. I don't like really hot drinks, so I usually put mine on a metal surface to cool down. Mind you, 9 times out of 10 I then forget about it anyway, so I could put it anywhere and it'd still go cold.

Regards,

Andrew