Member postings for Andrew Johnston

The Burnerd Multisize collet chuck sits on my lathe by default, unless I need the 4-jaw chuck or one of the faceplates.

Despite the skepticism I can assure Adam that they simply don't hold short parts. For lengths less than a quarter of the collet length the fingers simply tilt and one can pull the work out by hand. Up to about half collet length the work seems to be held ,but may well come out under cutting forces. More than half the collet length is fine. One solution is to use a short length of material at the back of the collet when using short work. But the spare material must be the same diameter as the work to within a thou or two otherwise the collet won't hold the work securely when it closes.

Andrew

All round bad idea. Think reciprocating mass. You may need to beef up the connecting rods.

Andrew

I try and avoid cutting compound for hand tapping as it's a PITA to remove from the hole and tap. But if needed for tough materials and/or large taps I use Rocol RTD. For machine tapping on the vertical mill dry or a squirt of WD40, especially for aluminium. Machine tapping on the repetition lathe uses flood soluble oil, simply because it's there.

Andrew

In the context of the OP I wouldn't regard systems having an encoder or resolver on the motor as positional closed loop. They still rely on the accuracy of the ballscrews for position accuracy, even if the motor itself is closed loop control. My comment was based on having an independent method of measuring table position, and using that in a closed loop control.

Andrew

Try cleaning the commutator with some fine abrasive on the copper and use a fine hook to clean out muck from between the commutator segments. Worked for me on the Bridgeport power feed DC motor.

Andrew

Most hobby stepper motor CNC mills and low end professional systems, even with servo motors and encoders, are open loop. So they rely on the inherent accuracy (or otherwise) of the ballscrews. High end professional CNC mills may well have independent measurement systems as an option and would therefore be closed loop.

Missed steps keep getting mentioned, but in over 10 years of CNC milling I've never knowingly missed steps; and I run my CNC mill fairly hard.

Andrew

If I recall correctly my challenge to SoD was to do with a statement that HSS and insert tooling remove metal in different ways. They don't; in both cases they shear metal from the work. There is significant distortion of the metal as it is removed which takes energy and manifests itself heat, Hence the saying that most of the energy used in removing metal is carried away in the swarf as heat.

Of course there are differences of degree between HSS and inserts. The moulded inserts tend to have a slightly rounded edge so they tend to be less good at shallow depths of cut and/or fine feed rates. But that isn't absolute, it depends upon material.

Arguments about the horsepower used by HSS or inserts is the wrong metric. What is of interest is the power needed per unit volume of metal removed. Since inserts can run at much higher temperatures than HSS as has been said the shear zone can be red hot. Hence the metal is soft and more easily sheared. The insert may need to be running fast and a high DOC and feedrate to achieve this. So the absolute power may be higher, but the power per unit volume may well be lower.

While I don't do it often I have had swarf on the both the lathe and mill coming off dull red in subdued light with carbide tooling. You definitely do not want that going down your shirt front!

Andrew

Here is my overarm support assembled:

And disassembled:

The hole in the housing is tapered, about 1/8" larger in diameter at the back.

Andrew

Quite common with larger flywheels, for a number of reasons:

The size of pattern and mould needed

The capacity of the foundry to melt and pour cast iron

Transportation of the flywheel to the customer. Moving something 30 feet long and 15 feet high is one thing. A 30 foot diameter part is a whole different ball game. Even with modern transport it'd be a challenge; there aren't many road bridges with a 30 foot high clearance!

Andrew

It looks a bit odd, but I think it is correct. Of course higher pressure angles are rarely used for spur gears as they result in flattened teeth which have a significant radial component to the contact force. Generally one only finds high pressure angles in multistart worm drives. Using high pressure angles in this case avoids serious undercutting of the worm wheel by the hob.

Andrew

If it helps I can photograph, and possibly disassemble, the support bearing for my Adock and Shipley 2E.

Andrew

It's instructive to look at the end of centre cutting endmill to gauge quality. A branded cutter will be very different to some cheap cutters, which won't centre cut and give a poor finish. In the past I used Garr cutters on my CNC mill. They were fine on aluminium but seemed to wear very quickly on low carbon steel, so I changed to Gunhring. To be fair the Garr cutters I used were uncoated carbide, so may not have been the best choice. I now use YG and the ARC premium range. Plus cutters from Drill Service for specials.

Andrew

Machinery's Handbook has tables of coarse, fine and constant pitches for metric threads, as well as 1st, 2nd and 3rd choices for nominal thread diameter.

Andrew

I agree with Gordon. I learnt to power fly on a Tiger Moth, so I've been signed off for hand swinging a propeller.When starting the Moth one used the right hand on the blade up and to the right (looking from the front) and swinging down. So definitely clockwise. As Gordon says, the opposite way to most Lycomings. It also means that the aircraft swings the other way on take off, which can be exciting if you forget and push the wrong rudder pedal.

Andrew

Looking good.

I might make one change. Using a 6mm ballnose cutter instead of a radius tip cutter would have given a better finish for a given stepdown, especially on the more vertical surfaces. Ideally one would vary the stepdown according to the slope of the work. Does Fusion360 have a command for scallop height rather than stepdown?

Andrew

In a word - no. Addendum and dedendum are determined by DP or Mod with an arbitrary addition to the dedendum for clearance. Of course at some point each tooth clashes with the adjacent tooth as PA increases.

Andrew

Yes, but SoD is a clever old sod, and has full diameter resistors that magically don't dissipate energy.

Andrew

Agreed, but it complicates the process, always assuming that the dividing mechanism is capable of indexing 2 or 4 times the tooth count. Looking at the excellent close up of the gears above I'd be more worried about the variation in tooth shape from tooth to tooth, particularly for the pinion. Not sure why that should be, but I doubt extra offset passes would help.

The question of undercutting has two strands. One, is undercutting needed to clear the mating tooth? Two, will a hob undercut whether it is needed or not? In theory the dedendum is the same as the addendum at one over the diametrical pitch. In practice some clearance is needed, common multiples are 1.125, 1.157 and 1.25. So the teeth on the hob will cut deeper than a mating gear tooth to give clearance. But the hob teeth may also create an undercut even though it's not needed for a mating gear tooth. It's important not to mix up need and effect.

Andrew

I can see two issues with that. One, there will be a variation in quenching due to mass and the inner leaves cooling via conduction to the outer leaves. Two, the recommendation for leaf springs is that all leaves have the same radius before assembly so they only touch at the ends before clamping. Clearly this won't be the case if the leaves are hardened and tempered together. So the spring may not behave as expected.

Andrew

Don't buy material from Ebay if you want reliable properties. Hardening temperature seems a tad low, I'd go to 780C. How thick is the material? Soaking for 40 minutes seems a long time. For rectangular sections it's the smallest dimension that sets the soak time, not the largest. Tempering temperature seems a bit high, I'd be around 300-310C. Can't help on the distortion as I haven't experienced it. Poor material may be?

Andrew