Member postings for Andrew Johnston

It's more dependent upon material. Cutters intended for aluminium often have high helix flutes. But they are only advantageous if one can run at the high speeds and feeds required. Similarly for tough materials cutters can have esoteric coatings and variable helix angle and/or flute spacing to reduce chatter. Again one needs a mill that is capable of utilising the features.

I don't regard my Bridgeport as being able to make proper use of the fancy cutters, so I don't buy them, other than polished cutters for aluminium.

Andrew

Depends what sort of reamer. Machine reamers cut on the leading chamfer, not on the flutes. So sharpening the chamfer should restore them to good condition. If they're hand reamers with a long taper it's more difficult to re-sharpen. Irrespective of type if a reamer can't be made to cut to size I'd recycle it.

Andrew

Too small a tapping drill, I use 3.5mm for M4 threads. Spiral point is better in the sense that it pushes the swarf ahead of the tap. But for smaller threads I prefer spiral flute as the swarf is ejected back out of the hole as a long spiral and without jamming. The long thread length doesn't help; does it need to be that long? I'd be looking at changing the design.

Andrew

Seems pretty straight forward for X and Y. I understand how he measures Z, but not sure why he chose the Haimer to be tool 1, or how this interacts with the tool table. I'm old hat and use a master tool, labelled 0, to set a zero for measuring tools for the tool table, and to set the work zero in Z. Modern thinking tends to use the spindle nose as a reference, but that can be a PITA to see what's going on. And in some applicastions is too large to be able to set the work zero in Z.

Andrew

Pathpilot has a fairly comprehensive set of probing utilities, but all reliant on an electronic probe. Can't see why I'd want to use a non-electronic probe? As far as I'm aware Renishaw probes work on conductive and non-conductive materials as does the Tormach active probe.

Andrew

Mine gets used more often on my manual mills than the CNC mill. I can't afford a Renishaw probe solely for the CNC mill, and even if I could, I wouldn't trust an addon for Mach3.

Andrew

Some statements by SoD need clarification.

A single wire has inductance, so as the frequency of a signal increases the resistance of the wire stays constant, but the impedance increases. One might argue that the effective resistance increases due to skin effect, just to pre-empt the experts.

The subject of EMC covers a wide range of areas. The main ones are radiated emissions, immunity to radiation, conducted emissions and ESD. If a device is mains powered then there are also mains borne nasties to be checked.

Radiated emissions are fairly simple to control, with the exception of cables. I hate cables inside, or external to, a product. Immunity is also fairly simple, especially for some applications, such as consumer, where the unit doesn't need to continue working, but just has to recover without damage. In other applications, automotive for instance, the unit needs to work throughout immunity tests. It's no good if the ECU hiccups every time a spark plug fires. Conducted emissions are fairly simple to control with appropriate filters and/or shielding.

A big cause of EMC test failure is ESD - it has a habit of getting into places it shouldn't, through pathways that one hadn't thought about.

Andrew

I suspect my path was somewhat different to the norm.

Over the years I'd seen small CNC mills pocketing out clock wheels and similar at exhibitions. But that really didn't interest me. Similarly I have the skills to convert my own CNC, but not the interest. I'm lazy and want to make parts, not faff about with machine projects.

The impetus to go CNC came from work, where I was doing the mechanical and electronics design for a high power bi-directional AC to DC power converter. Clearly the case and liquid cooled heatsink was going to need to be CNC milled. I looked at a number of options from new, or secondhand, professional to high end hobby. In the end I settled on Tormach. The criteria were a minimum envelope of 6" cubed (which in restrospect would have been far too small) and 4-axis. Of course I could see that the CNC mill would be useful for my traction engines as well.

I was already conversant with 3D CAD, so it was simply a matter of learning CAM. Suffice to say I ended up with VisualMill, although looking back I'm not sure that was the right decision. OneCNC might have been better. These are commercial packages, but remember I want to make parts in a sensible time so multiple tools, automatic tool length measurement and tool tables, plus 2.5D, 3D and 4th axis capability were essential. Re-machining capability is essential for me.

Learning CAM and CNC was a very steep learning curve done under extreme time pressure from the client. Within a few weeks (full time) I was comfortable making fairly complex 2.5D and 3D parts. I can't show many of the larger parts, but here are some of the simple parts I made while feeling my way:

Subsequently I've made many parts for work and for my engines. The engine parts range from simple but where multiple parts are needed like wheel spokes to parts that would be difficult to make in the workshop by other means:

or impossible:

Like everything else the CNC mill is a tool to be used when appropriate. I don't have a CNC lathe, but my repetition lathe is probably quicker at turning out the multiple parts I need such as nuts, bolts and studs.

Andrew

I suspect margins on the machines are low and the cost of support with users adding their own computers and CAM software is high. Let alone when the electronics play up.

Andrew

That's what I did - bought the plans and then decided what machines to buy. The swing of the lathe was set by the flywheel and the distance between centres by the front/rear axles. To some extent it depends upon how much the OP wants to do himself. Making spur, bevel and worm gears for instance will dictate sizes and capability. I had to drill/bore the hornplates for my engines in several steps as the Bridgeport wasn't big enough, particularly in Y. I didn't turn my wheels but made them by the fudgeit and bodgeit method and hoping for the best. Most spoke/strake holes were freehand drilled, but I had to get creative for the first row of strake holes, even with a 12" rotary table:

The biggest issue will be Z, followed by Y and then X. I've run out of Z several times and have needed to buy stub drills/mills or collets. I've also run out of Y a few times, but X only when machining the rear rims before rolling:

I also ran out of Z on the horizontal when cutting the final drive gears:

i suspect size of mill will be dictated by a 2" scale traction engine - in general parts for a 5" gauge loco will be smaller. I'd also echo SoDs note about clamping. It can take up a surprising amount of space/travel, not just on the mill but also on the rotary table.

Andrew

Actually they're in the entrance hall. They were in the kitchen, but after a complete refit a couple of years ago i was told no way they're were going back. And you don't argue with my mum! The sitting room is for work in progress and parts waiting to be fitted:

Andrew

i suspect that's nonsense. A lathe with a proper backgear should have full power available at the spindle, whereas with a DC motor running at slower speed will not provide full power. In this case the cut is limited by the weedy boring bar:

Flywheel diameter is 16.5" and is running at 40rpm with DOC of 0.06" and feed of 0.01" per rev. That's about 1.25 cubic inches per minute, well below what the lathe can do, but limited by the boring bar. Not allowing for transmission losses the available torque is over 500Nm. Metal removal rate is almost all about available power at the spindle.

Andrew

They are available for some ex-industrial vertical mills:

But they seem to go for silly money these days and are no where near as rigid as a proper horizontal.

Andrew

Good grief - I never thought it would happen, but I agree with SoD!

I have both vertical and horizontal mills, and in both cases the accessories to convert to the other mode. But I'd agree with SoD that the vertical mill is the more versatile. In particular for drilling the quill is all bar essential. While vertical heads for horizontal mills can have quills they seem to be pretty rare. I've just looked at the manual for my horizontal mill (Adcock & Shipley) and there is no option for a vertical head with quill.

Another point to note is that travels on a horizontal mill are small compared to the size of mill. For instance my vertical mill weighs about a ton, is 1.5hp, and has travels of 33" and 12" in X and Y respectively. Whereas the horizontal mill weighs nearly 2 tons, is 5hp, but only has travels of 23" and 8" in X and Y. Vertical travel is the same on both at 16".

The horizontal mill is way more rigid than the vertical mill and that is excellent when gear cutting and where lots of metal needs to be removed. Horizontal mills are pretty much obsolete commercially and so secondhand ones are cheap - mine was £175 compared to £2k for the vertical.

I wouldn't like to be without either, but if I had to give up one it would have to be the horizontal mill.

Andrew

Could use a roller box.

Andrew

Pity we can't administer some Chinese justice.

Andrew

It shouldn't be a problem with a continuous gate voltage applied, but triacs have a holding current. If the current through the main terminals drops below the holding current then the device turns off. But that usually only applies if the gate voltage has been removed.

My best guess is that the output waveform is badly distorted. It's going some to make a toroid buzz. I agree with using a 'scope to look at all signals, input and output.

Andrew

I've just read the AAIB report; as Peter says the aircraft was a touring motor glider. So more akin to a powered aircraft than a sailplane. I think current licencing distinguishes between self-launching sailplanes and touring motor gliders. I flew a Falke while doing my instructor training - not much to write home about.

Sailplanes and motors are now rather messy. Most self-sustainer engines are retractable. At one time the engine moved out on a pylon with direct drive to a propeller and is normally air start, as is my Nimbus 3DT. Some self-launchers extend the propeller but the engine stays in the fuselage, driving via a belt. This simplifies the pylon design, but is primarily for noise reasons. There are sailplanes that have a motor in the nose and a small propeller at the front where the blades fold back into recesses when not being used.

Tradtionally motors were 2-stroke petrol. But there are now also small jets and of course electric. The jets are impressive, but have the problem of inefficiency inherent in small gas turbines. Electric is a mixed bag. It promises much but so far doesn't quite seem to deliver. And of course battery fires are an ever present problem. There have been a number on the ground but I haven't heard of one in the air, as yet.

Andrew

That's useful to know. It'll save me wasting time on a none existent problem. It might be prudent to put your seatbelt on though.

Andrew

In magnetic terms 0.1mm is a pretty big gap. With the existing design and kit available I think you'll be wasting your time. Far better to invest that time in coming up with a better design. Why can't the part be bent from a single blank? Even if the angles could be made accurately how are you going to hold the parts together? Ferrite cores, gapped or otherwise, come with stiff springs to hold them together for a good reason.

Andrew