Member postings for Ajohnw

I use 10mm tooling or down to 1/4 hss on my boxford and don't get problems with the tool flexing. I do get a bit of a bearing problem due to the front one wearing a little oval so it can't be tightened to correct that and like everybody on any lathe the work can bend.

I spent a couple of months one a dsg once using 5/16" hss in a holder. No problems from flexure at all and a finish like glass. Material supplied would generally allow 3 cuts to finish to size circa 0.1" off the diameter or more each time. The trick to finishing exactly on size to a few 1/10 thou or better is to note how much the 2nd cut actually took off and aim to make both the 2nd and last cuts the same size. Or improve further given the sufficient material increase the number of cuts.

Only problem with that is that the lathe wasn't very old and only a couple of people a year used it for a month. I did 2 due to being picked to do international turning test. The other aspect is that the lathe was in such good condition and quality on this particular model that it was perfectly capable of taking miniscule cuts down to a few thou even to the extent of finishing things off that had an 0.015" grinding allowance left on them bang on size without any problems at all. Some lathes due to wear and headstock design just wont sensibly do this sort of thing hence the cut sizes we were told to think about. Some need it but it's a shame about the taper even as little as it is. More wear and even this wont work.

On the other hand take a lathe that 20 odd people used for a week every year and had been around for some time and nothing could be done about the rings that appeared in the work as it was all small stuff circa 1/2" dia and less and the fact that the headstock bearings were not adjustable so out comes the emery cloth.

John

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Freaks is the right thing to have on the end of the name. It's interesting to put a current sense on the supply on a circuit like that but few people have anything suitable - high frequency hall effect oscilloscope probe as both mosfets will be on for short periods as they are switched. They have sort of done something about the problems that is likely to cause on the supply almost certainly adding more parts than if the drive had been done correctly.

90nSec rise times are good at generating RFI especially with long lengths of wire on them. No need so why switch that quickly unless it's needed. The actual rise times might turn out faster that that. I'd hope that the data sheets have pulse thermal resistance info otherwise guess.

The absolute maximum rating of the i/o pins on the processor is 40ma however the max for the chip is 200ma. They point out that these aren't what might be called real absolute ratings as long term use might damage the device or cause premature failure and later reduce them to 50% as far as the pins are concerned.

Often on electronic items spec's are given in regions that they are expected to work in. As far as output is concerned that's 3ma but on this sort of part that can be exceeded providing the totals are looked at. The i/o conditions that the device can stand are given in condition 3&4 on page 317 of the full data. Essentially 100ma per port by the look of it and 20ma per pin - they don't mention the chip limit when driving which is likely to be 100ma max in practical terms with near 10 running the processor.

The reason for putting something in the way when driving mosfets is the capacitance in them. It's possible for the processor pin to get volts forced onto it back through the mosfet. The ports do have clamp diodes but it looks like they are for ESD protection only as they don't specify a max current through them. Processors turn into thyristors if the port input voltage range is exceeded. A puff of smoke, a nasty smell comes out and a small hole appears in the package. Not terribly likely in this case but it can happen. Pull down resistor can help a bit even the usual 20k because it may happen when they are inputs. Looks like high side drivers ideally need pull downs as well. I'd have thought that they would build them into the chip as no one wants to add more bits. It's annoying. Lots of things need them to define what happens during reset and before the post is set to the correct state.

John

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Great idea as they have lower saturation voltages. Certain ZTX's are way way better than BC017's as an alternative. One of them can be used as a high side switch too - however ........................

I have a few germanium bits about too. They came with an Xmas present when I was around 8 or 9. My electronic set. Had an electric one the year before but motors/dynamos and shocking coils etc get boring after a while. All of that one has unfortunately gone, most of the other too. I never thought of it as a career but strangely finished up doing rather a lot of it at times.

John

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Edited By John W1 on 25/11/2015 10:44:52

Best not let you work on any ABS controllers then Neil.

Meant to add - a board like that with 3 stepper drivers and a couple of switched output may be of interest in other areas.

John

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Edited By John W1 on 25/11/2015 10:10:58

Correct

To set the gibs remove the lead screw and slide and apply some slide way oil. Put the slide back on and adjust the gibs for slight resistance to movement pushed by hand then refit the lead screw. On lathes like the shereline the same should be done to the saddle as it can and will tilt when it's moved back and forth. It's a problem with dovetail beds. Sometimes it helps as the tool may move away from the work when it's wound back - rare.

Usually if the bearings are severely loose the same cut setting will remove metal rather than just scrape on several passes. It will remove more metal right up to the end of the cut but more at the end of the work. Any looseness causes the same problem. Generally if some wear and they are only slightly loose running the same cut again can spoil the finish. Many lathes have a minimum cut which will produce the best finish. It will change with diameter of the work. That aspect makes hand feeding more difficult as each time the rate changes marks will be produced on the work. Usually rings. The same thing can happen when using power feed especially when too light a cut is taken or when the feed rate is too low.

If say 2" of 1/2" bar is turned the metal may bend while it's being cut. If the same cut is run again more metal will be removed at the end but it will turn into something more like scraping as the tool gets nearer the chuck.

If no bending and decent bearing settings running the same cut again will be more like a very light scraping. The finish might look worse in some respects but the actual depth of the defects will be improved.

Another problem with tiny lathes is the the lathe itself may distort. If everything is basically ok then running the same cut again is likely to give a good finish.

My only experience of using lathes of this size is with a Taig / Peatol. Nothing bends on these as there is a strip of concrete under the bed. I'd assume that area isn't a problem on Sherelines. Set up correctly as new and with a suitable tool they can produce a finish like glass on materials like free cutting mild steel. Some materials such as silver steel tend to tear what ever lathe they are on but in terms of um depth of defects the finish can still be pretty good for a lathe. Some cast iron can have the same problem.

Really any serious book on turning should go through all of this so that people can sort things out to suite the lathe they happen to have.

John

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It up to you Neil not me. As for instance looking at ab IR golden oldy

**LINK**

More expensive but I would be thinking in terms of something like this.

**LINK**

Max switching frequency about 3khz - way way to high, drive series resistance 4 to 10K. There has been some debate in astro circles about using low side drivers when these are available.

In TO220 they start at 5amps as shown here

**LINK**

In surface mount, some are easy to hand solder, there will be more available and some pcb copper can be used as a heatsink. There is info about on their web site about that, often in the data sheets but I have only ever needed to look at that on straight ordinary mosfets.

John

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It looks to be a bit cheaper off ebay with a world wide search.

John

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Edited By John W1 on 24/11/2015 21:40:01

That looks like this one. $55 of amazon

**LINK**

John

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They show drive currents up to 20ma per pin but some where in the data sheet there will be a limit on total drive current across all ports - well there should be but I can't see one so if at work I would ask.

A bit naughty on the mosfets Neil. The port pins are floating during reset and till you do something with them so there should be pull down resistors. Where I come from there would probably be a cheap inverter in the way back to the processor and a pull up resister on the front of that, The port pins do have clamp diodes on them though so should be ok without the additional gate. I'd looks and see how well the fets switch with 2k in the gate circuit and not go lower unless really needed.

The automotive industry use truck loads of IR avalanche rated logic level mosfets for solenoid driving, hence some being dirt cheap. No clamp diode needed for inductive loads. Increasingly high side drives are used from the same source so some of those should be dirt cheap too. You may well find these have other advantages ie pull ups and resistors in the way etc. Things have gone that way as it keeps the power source in the ECU rather than trailing about all over the place.

John

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OTT, either over twenty one tiswas or over the top.

John

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It might be worth you having a small bottle of cutting oil around Brian. You could use all sorts of things some specific to the materials you are working but that's a bit OTT really. On a reamer for instance just smear a little on with a small brush. It will help get an H7 tolerance and improve the finish. You should find it on ebay Oz. It oxidises and rapidly so keep the screw cap on the bottle except when you get a little on a small brush. Something like a 1/4" wide artists brush will take up more than enough of it.

I've not built a Stirling engine but my understanding is that there is zero friction from the piston. They have clearance according to the design and the motions prevent the pistons from actually touching the cylinders. That aspect needs a high degree of precision.

I've resisted building any sort of engine for a long time but of late am weakening.

John

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It sounds to me that the best and quickest option would be to grip some pieces of strip between rather than in the jaws and then grind them individually by rocking the chuck by hand.

Very light cuts, maybe 1 thou at a time to help reduce grinding wheel wear as you may not be able to feed the wheel entirely through the jaws. Dressing the wheel somehow with a diamond point fixed in place wouldn't be a bad idea.

John

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I think I just found what look to be the castings for the universal pillar tool. They must have come with my boxford, 12+ years ago and I didn't notice.

As I have to go to the top of a 3 story house to use the bench drill one that small that could drill a 1/4", maybe 5/16" hole would take care of most of the metal drilling I do.

As if I haven't enough to do.

John

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Any lathe I have seen has the pinion within the width of the saddle which to me makes a lot of sense. Except the ML10 probably because there was no room to get it anywhere else. That uses a helical type gear / worm wheel running on the lead screw that also functions as a screw cutting indicator even on the metric ones.

The parts take a lot of stick and have to maintain an accurate alignment so I would most definitely make separates housings to carry the shafts and mount those on the apron.

John

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This page goes through the various option for wiring one of these for fwd/off/rev.

**LINK**

The same is true of other makes as well but the labelling can differ.

John

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I would miss the headroom that's available on a bench drill compared with small milling machines. Not needed that often but when it is ............................

One thing you could do is look at replacing the bearings in your drill and tucking it away some where for if and when you need it. Some do have bearings. Some just run in plain ones which can be hard to fix.

I have an adapter to fit my face plate or chuck to the tailstock of my lathe. Used pretty infrequently but there is plenty head room.

John

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According to lathes co uk it should be fitted with a 1/2 to 3/4 hp motor either 1400 or 2800 rpm. The higher speed motor might only relate to more recent versions. I would have said that even with morse 2 a 1/2hp motor is preferable.

Personally with a 6 speed gearbox built in I wouldn't bother going to 3 phase and an inverter but would wonder about fitting a single phase 2800rpm motor and would stick with 1400 rpm.

It's possible to buy fwd / off / rev switches. For instance

**LINK**

Really there should be a no volts release switch in circuit before these to meet modern safety standards however there will be older machines about where people have to remember to use the switch to turn it off if there is a power supply interruption.

The 3/4hp option is probably for when a 2,800 rpm motor is fitted. Lathes co aren't clear on that point.

John

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Edited By John W1 on 22/11/2015 11:31:50

Edited By John W1 on 22/11/2015 11:37:16

A flange

but the part the shaft fits in needs to be longer on yours. I would make it 1 1/2 to 2 times the diameter of the shaft long. The larger diameter needs to be big enough to transfer the load to to wood. ie plenty of distance between the fixings.

John

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There are a lot of them. So which ones

**LINK**

John

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I'm pretty sure my Dad made his during his apprenticeship. Tidier than yours Jason. No thread sticking out of the end when fully closed. I'd say the jaws formed a bit more of a squarer when together and there were flanges where the handles meet the jaws. I tried to find it after he died but it had gone, no idea where.

I made 2. One for the small stuff, V filed in the side of a drilled hole and a usual type with a sliding jaw to one side. One of the more useful test pieces. Filing out the slot and filing and fitting the jaws.

John

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