Member postings for Andrew Johnston

I use the nominal thread diameter. That's true whatever method is used to form the thread - single point screwcutting, Coventry diehead, or split dies by hand and under power on the repetition lathe.

Andrew

You'd be best advised to keep your wild guesses to yourself (wagging finger). I've been known to use the allegedly pejorative name in question. I've bought hundreds of items over the last 20+ years ranging from 99p for a box of bent taps to over £1000 for a cylindrical grinder. I've had very few issues, one or two none deliveries and a couple of cutters described as new which had clearly been reground to the limit. All sorted with no problems. I always do my research on items and sellers. If needs be I'll ask a question and judge the response. A response along the lines of "selling it for a mate/part of a job lot/don't know anything about it" means I don't bid.

I've also sold items, mostly surplus electronics and a couple of cars. Only had one real problem with one of the cars. Why would someone from Poland bid for an old undesirable car (Xantia) that was advertised as having a starting problem? I never did work out the scam but I told them that unless they could provide a verifiable UK address I wasn't going to sell to them. Never heard from them again. I eventually sold it to the second highest bidder who repaired cars as a sideline and whose brother worked for Citroen, so it was simple to get spares.

I use Ebay a lot less than I used to. One, I've got most of what I need, or have space for. Two, it's much more commercial now with many unrealistic prices. I keep a lookout for the few things I'd like and look for specific cutters or similar when I only need it for one job and don't want to pay for new.

You owe me an apology, as does Ramon.

Andrew

Back in the 1990s when I was working full time on designing the power electronics for electric vehicles we started with simple induction motors (up to 100kW) and full vector control, ie, a VFD. One thing an electric vehicle needs is full torque at zero speed which makes the controller a bit more upmarket than VFDs intended for machine tools. We then modified the software to deal with trapezoidal motors aka brushless DC. We then did another tweak for permanent magnet motors, similar to BLDC motors. We used off the shelf commercial motors, which were large. Now motors are much better tuned to the application. Like IC engines electric motors in cars rarely run at full power for any significant period of time, so the motors can be small compared to full rated motors. We used a single motor per vehicle, apart from buses where we needed two motors gearbox coupled to get the power. These days each wheel tends to have it's own motor which can be smaller and dispenses with the need for gearboxes and differentials.

We did a project with Oxford University with a weird kind of induction motor that had 10 poles and 12 windings, or the other way round, can't remember which. I never did get to the bottom of understanding how it worked.

I think modern vehicles use a mix of induction and BLDC. If anything the battery management system is more important. One thing we discovered early on is that one needs to monitor each cell and use a charge balancing algorithm. Otherwise the batteries get out of kilter and one ends up overcharging or over-discharging individual batteries.

Electric gliders mostly use BLDC for self-sustainers but the only self-launching glider we have at our site uses an induction motor (I think).

Andrew

Edited By Andrew Johnston on 28/11/2020 14:47:14

Posted by IanT on 28/11/2020 12:18:46in.

Am I correct in this assumption or am I missing some basic difference between the two tools?

Be careful. A taper pin reamer is like a normal parallel reamer with positive rake cutting edges. A clockmakers broach may be of polygonal (usually 5 sides) shape where the "cutting" edges have a large negative rake.

I think there was a thread on this a while back, but I can't immediately find it.

Andrew

I've always used taper reamers by hand and dry, which means no mess to clean up. I set the hole size to drill by measuring the diameter of the pin a bit up from the small end where I think it will actually exit the hole. i agree that the key is light axial pressure and frequent withdrawals. Towards the end the reamer is cutting over nearly the full length. One can "feel" the reamer cutting or shaving really. The steel swarf I got was very fine,almost like a powder. Don't forget to check with the pin at frequent intervals. It's easy to make a turn or two too many with the result that the pin will stick through too far. If anything stop early. In use the pin will be tapped home and so will go in further than quick check by hand would suggest.

Andrew

Jouke,

I know of Almelo although I've never been there. I can't remember if the train from Schipol went through there before Hengelo or was direct from Apeldoorn.

My work on pulse compression radar was purely at Cambridge. During my time in Enschede I was working for Ericsson as a subcontractor from an engineering consultancy in Cambridge. We worked on an early tablet. The project never went anywhere; although a good idea the technology at the time wasn't up to the job, coupled with appalling company project management. The Ericsson factory was right next to the football stadium and station at Drienerlo. I was very impressed with Dutch trains. Fast, clean, cheap and on time to the second. I was working in Enschede around the time the fireworks factory blew up and flattened a good bit of the surrounding suburb, although not there to witness the actual explosion.

Andrew

I bought my small taper pin reamers from Drill Service. The 1/16" reamer is listed at £20. Brand is Trubor; claims to be UK made. Mine have worked fine in steel. I work on the principle that Drill Service supply the professionals and they wouldn't last long selling carp.

Andrew

Long lead helical milling is simple enough using a universal mill and dividing head:

Or on a vertical mill with right angle head for short leads:

For the short lead gear the table feed couldn't drive the table via the speed increasing gear train. So the gear was cut by turning the dividing head and using that to drive the table. Some universal dividing head manufacturers sold short lead attachments. They're nothing fancy. It just means the table leadscrew drives the dividing head spindle directly rather than via the worm and worm wheel. The end of the dividing head spindle is in the middle of the picture above. For short leads one simply drives an expanding arbor in the hole via a gear train directly from the table. Some of the resulting gears:

Although my lathe (4 tpi leadscrew) will cut a 2 tpi thread I chose to use a CNC mill when I needed a 2 tpi worm:

The worms:

In the absence of smartypants equipment I'd be with Rod; use the lathe but using the leadscrew to drive the spindle. Whether one uses a single point lathe tool to cut the thread or a milling spindle would depend upon the thread form. A square thread could use either method but Acme, V or buttress might be simpler with a single point tool.

The problem with Rod's method for cutting a short lead tap is that the milling cutter needs to be larger diameter than the milling spindle so the tap can pass under the milling spindle. Again milling machine manufacturers used to advertise short lead or rack milling heads which had a small diameter to pass over the work while still being able to cut the thread, or rack.

Andrew

Define precision.

I wouldn't call radius cutters a precision tool. Let's ignore the confusion and assume we're talking about a cutter with a radius of 15mm. That's potentially a pretty large width of cut. I doubt a small milling machine will be happy. I don't have any radius cutters that are used vertically. But I picked up a set of radius cutters for the horizontal mill some years back. They work well:

But you need a rigid setup to avoid chatter and a poor finish. I only use them for making parts look pretty. If I needed a precision radius I'd use a ball mill on the CNC mill with a 3D adaptive stepover. In the absence of a CNC mill I'd use a rotary table as mentioned above.

A problem with using the above methods (except CNC) is that it is easy to go a thou or so too far with the cut. This leaves a small ledge or indent on the work which is suprisingly difficult to remove by filing. By the way I can't see sandpaper having much effect on gauge plate. Better to use emery cloth.

The method of rotating the work in a vice and using an endmill to produce a series of flats has never worked for me.

Andrew

Why do the computer modellers assume that a temperature change will be universally disastrous?

Andrew

Given it's a pivot hole for a motor, presumably with little or no axial loading, I'd just drill a hole and be done with it.

Andrew

I can't speak for Oxford as I didn't go there, but I'm not sure your boss was correct about Cambridge. At undergraduate level Cambridge is unusual in that all undergraduate degrees lead to a BA, irrespective of subject. An MA at Cambridge isn't issued on the basis of exams, it's awarded as a matter of course to those with a BA after meeting certain administrative requirements. There were M.Phil degrees awarded by study and research. When I was there (1980s) postgraduates normally started on a Ph.D. and if one didn't make the grade at the end of year one you were given an M.Phil and asked to leave. It seems to be radically different now. There are many taught courses at Masters level and it is mandatory to have done some of these courses before commencing a Ph.D. I'm not convinced that's a good move. When I started I'd never heard of pulse compression radar, but at least it meant I began my research without any preconceived ideas.

I worked for a while in Enschede; I remember passing the Technische Hogeschool when walking to and from the railway station and my preferred hotel. I assume that was different from the University of Twente (?) which was over the road from the factory where I was working.

Andrew

Ho hum, another dispiriting thread leading to the usual disparaging remarks. Since I've been an academic in the past according to the experts on here I must be practically useless. So I'm going to have to come clean; all the pictures in my albums have been photoshopped.

Andrew

No, it should be perfectly possible. However, slot drills are ground slightly concave on the end, so if you want a truly flat bottom to the hole you'll need to make your own D-bit. Here's a secondhand 1" slot drill making a hole 1.5" deep:

The hole was predrilled 9/16" as that size goes deeper than the 1" diameter anyway. The hole measures 1.001". So it is possible. To the notes from Ady1 I'd add cheap cutters. If a 5.9mm drill produces a 6mm hole then something is wrong. Out of interest I just measured a hole I drilled 6.4mm a while back. It measures 6.42mm. I was using a quality 4-facet drill from Dormer. My guess would be that the problem is caused by poor quality cutting tools and/or tooling.

Andrew

I've used the Bridgeport quill to drive a 1/8" broach in cast iron:

But I was pushing my luck and wouldn't do it again. Although I now have a proper arbor press broaches can still be fiddly:

I cut the internal splines (5/16" wide) on my traction engine gears (EN24) using a home made HSS cutter and a slotting head on the Bridgeport:

This was a trial run on an embryo gear I fudged up. The end of the tool is curved to match the external spline:

Given that a shaper is available there's no question that it should be used.

Andrew

Both engines are now on their wheels:

To be precise the engine with rubber tyres is actually sitting on wooden blocks. They may be here for some time and I don't want to risk flats on the rubber wheels.

Andrew

That's what I mostly use. I have used a rotary table for rounding ends, but I'm not a fan of the method. It's too darn easy to go a gnats whatsit too far leaving a slight indent in the straight edge. Once done it seems to need an inordinate amount of filing to get rid of the indent. With filing buttons it's much easier to blend the curve and straights, even if everything isn't quite perfectly aligned. I'm in the "filing buttons are unhardened and recycled after the job is complete" school.

Andrew

There seems to be some confusion about the purpose of an input EMC filter. It is not there to reduce radiated emissions, but to reduce conducted emissions. So the fact that a radio works nearby is irrelevant. The filter should also protect the VFD from spikes and noise on the mains.

The filter should prevent high frequency noise from the VFD reaching the mains. It should also help with harmonic currents. Simple diode/capacitor rectifiers draw current in short pulses, which has many harmonics. From the generators point of view this is bad. So there are regulations limiting the current harmonics caused by equipment. Larger and/or more expensive VFDs will have a power factor corrector (PFC) at the front end which causes current to be drawn in proportion to the voltage, ie, the current draw will be sinusoidal. In the absence of a PFC the input filter will reduce the current harmonics by passive means.

I fitted a VFD to my CNC mill to drive the separate high speed spindle. Since the VFD didn't have an inbuilt PFC I fitted an external filter. The VFD and spindle were bought as a package from ARC. I've never had a problem with RCDs tripping.

Connection of the shield for the motor connections is a controversial subject. Should the shield be grounded at both ends or just at the VFD? On the high speed spindle I grounded at the VFD end only. While running in the spindle bearings a check with a spectrum analyser didn't show any significant radiated emissions, at least above 1MHz:

Andrew

That's what I do. I tend to buy secondhand cutters when I need a specific size that I'm unlikely to need again. As an example I recently used a 7/8" machine reamer to clean out the bronze bushes on my traction engine front wheels after loctiting them in place. Not something I'm likely to need again and no way I could afford a new reamer. So I bought secondhand at auction. Quality brand (Dormer) and it's a matter of judgement as to the veracity of the vendor. I've formulated a set of informal 'rules' to select vendors. But I've bought hundreds of tools on auction sites and have rarely been disappointed. In a couple of cases I've got my money back for cutters not as described.

Andrew

If I was going to make the part I'd use a hydraulic copy attachment:

But I agree with Jeff, change the design to something simpler. I made this in less than 10 minutes to demonstrate to a forum member how to make something with nowt more than a rule when dimensions are not important:

In industry I would think that ball handles are frowned on as one can get caught up in them and it's difficult to disentangle oneself.

Andrew