Member postings for Andrew Johnston

In theory this method should work in a similar manner to a Sunderland gear planer. The biggest difference is that the method indexes one tooth at a time. Whereas a Sunderland gear planer moves the cutter, and rotates the blank, by a small fraction of a tooth per cut. So the planer creates many more facets per tooth. Of course on the planer the cutter has to be set back a known amount every so often. One tooth space would be logical.

The method as described should work better on larger gears, as the involute has less curvature and the teeth are in contact with the cutter over more index steps. This seems to be borne out by the linked to pages.The smaller gears look very odd with lopsided teeth, unevenly spaced, whereas the larger gears seem better. The meshing of large and small gears seems odd too.This is the sort of meshing I'd expect to achieve, a thou or two backlash, albeit for larger 16DP gears:

If I was going to use this method I'd make the top of each tooth much shorter and add relief with a file before hardening. That was done on this worm wheel free hob and it seemed to cut well:

Note that the teeth are on a helix although the flutes are straight. I'd also make the hob as large as possible with no reduced shank.That just reduces rigidity.

It would be interesting to see some close up shots of the teeth and meshing on the gears by Neil.

Andrew

Andrew

As far as I can see it's a bog standard 230V single phase in and 230V 3-phase out. Interesting that the output frequency goes to 600Hz though. Even more interesting is that RS list it as non-compliant.

Andrew

Too right! That's one reason I don't watch much on Youtube. In a 30 minute video you get an introductory 15 minutes of waffle and not a machine tool in sight. At which point I've usually lost the will to live.

With the exception of the lathe top slide all my machine tool gibs are tapered. I adjust for a slight drag when using the handle. I always check full movement as it's not uncommon for me to use full table travel. On the Bridgeport things get tight at the ends, but I'm pretty sure that's due to the leadscrew/nuts not the slideways.

Andrew

Here's a link to a thread discussing the kit:

**LINK**

Not surprisingly the thread took a dive when an ex-member with an inflated ego took a swipe at people. Having tried the kit my conclusion was that I wouldn't buy for the reasons given.

Andrew

It happens to us all. I knocked a cup of coffee over my keyboard this morning and I'm only just back up and running. Although to be fair in the meantime I've also had lunch, gone for an 8 mile cycle ride and had a long sulk sitting out in the garden.

SoD has it nailed! Some playing with the numbers gives:

153600/128 = 1200

or 1200 baud for the serial comms. The measured value of 1.23kHz is pretty close allowing for measurement error and tiddly crystals that aren't that accurate.

I hate zebra strips. Many years ago in the mad world of motor racing the company I worked for used them to connect the electronics to the graphics LCD display on a handheld unit. The build instructions consisted of assembling the unit, seeing if the LCD worked and if not dis-assembling and repeating until it did. Mind you the draughtsman/mechanical 'designer' was incompetent and got the heave ho shortly afterwards.

Andrew

You're now guessing it's a tool problem and you plan to splash the cash on the basis of a guess? First, try a different piece of material. In the OP it's stated you know nothing about the material - therein lies the problem. Get some known free machining material and try it.

Andrew

Bit higher that I expected, but almost certainly related to comms or LCD data rate. Incidentally:

3 x 512 = 1536

so definitely powers of 2 come into it.

SoD: Your task for tomorrow is to stick the 'scope on the comms and see what the bit rate looks like.

Andrew

Some of the confusion arises from the fact that both RCD and overload functions use letters to determine the details, even though the functions are different and may be different parts.

If we look first at the overload function there are three common classes B, C and D. Class B will trip at 3 to 5 times rated current and is normally used in domestic properties. Class C trips between 5 and 10 times the rated current and is normally used in commercial properties. Class D trips between 10 and 20 times the rated current and is normally used in industrial properties. Class C and D are used where larger inrush currents are expected. All the breakers in my fairly new consumer unit are type B overload curve.

Confusingly the RCD function also uses letters to determine characteristics. The three most common are AC, A and B! Type AC only responds to AC residual currents. Type A also responds to pulsating DC currents and type B further responds to smooth DC currents. So in theory a VFD should be running from type B. But this makes it more likely the RCD will trip as it responds to more types of inbalance. Of course that might be seen as a good thing. The RCDs in my consumer unit are type AC and I run two VFDs on my CNC mill with no problems. Never had an RCD or overload trip.

Both VFDs run via EMI filters which contain a common mode choke and common mode and differential mode capacitors, but do not contain MOVs or transzorbs to catch mains spikes. Of course the filter components will attenuate mains spikes to some extent, but fast spike attenuation is left to the user, at least on the VFD I installed. I live in a rural area with overhead 3-phase feeders and fingers crossed I haven't had a spike related blow up yet.

Andrew

I suspect that what I did isn't relevant. Looking at the manual I changed a parameter in a settings folder to get a specific frequency shown on the VFD display. So clearly I'm running an induction motor. I don't know what motor the Sieg machines use.

Andrew

I'd be surprised if the clock frequency is more than a few kilohertz. The process isn't doing anything particularly fast or complicated so a high clock speed isn't needed. In CMOS circuits the dynamic power consumption is proportional to frequency and the supply voltage squared.

Think I'll stick to using mechanical micrometers - no batteries needed. I don't trust all this electronics nonsense.

Andrew

Edited By Andrew Johnston on 09/04/2020 19:05:15

Brass is very forgiving, so it should be fine at slower speeds with a commensurate reduction in feedrate. The tool looks like it is quite pointed. Put a nice radius on the end.

Andrew

I managed to fine tune spindle speed some years ago in Mach3 and I don't recall it being that difficult. However I was using the Tormach version of Mach3, so that might have been subtly different. I no longer have the system as I now use Tormach PathPilot; altogether leaps and bounds ahead of Mach3. I'm amazed the speeds are so far out. I think mine were only a percent or two. I wanted them accurate for use with a tension/compression tapping head.

Andrew

I'd use 1200rpm, 1700rpm is nearer recommended but the gears in my headstock start to get a bit noisy. Not good when you live in a quiet rural village - even quieter at the moment.

Andrew

A few more notes:

It helps greatly to use quality cutters - currently I use YG K2 and ALU-POWER cutters from Cutwel (open and shipping) and premium cutters from Arc (closed).

I wouldn't use MDF as a base with, presumably wood screws? If I need a base I always use steel or aluminium; although I do have fairly large offcuts piles for both materials

The most widely available aluminium alloy is 6082 (aka HE30) which machines very well

WD40 is good to prevent the swarf building up on the tool but doesn't do much for cooling. But for aluminium you don't need to worry about cooling. I use flood coolant on my CNC mill - for aluminium it's primarily for washing away swarf rather than cooling. For slotting I wouldn't use squirts of ED40, it'll just cause the swarf to stay in the slot. If the worst comes to the worst I machine dry and follow the cutter with a bendy straw or the vacuum cleaner to remove swarf. If you have a compressor you might be able to setup an airblast. But beware of flying swarf - a trip to A&E to get swarf out of the eye may be a problem at the moment. Of course you wear eye protection?

Andrew

I'd agree with Jason. I'd drill the two holes on the manual mill, screw to a fixture on the CNC mill and then profile the outside with a 3-flute 6mm cutter, full depth, 7000rpm, 400mm/min and 3mm width of cut. I normally leave around 0.5mm when roughing and then a full depth finish pass. For roughing I use climb and conventional milling, for finishing mostly climb. If the small concave radii can't be designed out I'd re-machine them after profiling with a smaller cutter. Make the cutter smaller than the radius to be machined or the cutter will chatter.

Generally I avoid slotting where possible. Even with flood coolant it's a PITA to clear the swarf and nothing fudges the cutter and finish quicker than recutting swarf. Another issue with slotting is the use of bridges. When I have to use them I make them 0.5mm high maximum. But they're still a pain to clean up. It can be easier to start with material slightly thicker than needed, profile the part, turn over and face off the unwanted material.

These parts are steel, but show the sort of finish that is possible with a hobby CNC mill:

Andrew

That's a relief; I was beginning to think I might be giving Pigpen a run for his money.

Andrew

SoD: Ok as far as it goes. But I'd expect the problem to be due to noise direct from the DC-DC converter, not external pickup.

Andrew

Resistor in series or parallel? Putting the capacitor at the battery terminals creates a low pass filter with the resistance of the wire to the converter output, which may be just emough to reduce switching noise.

Andrew

At least I'm not ignorant.

Andrew