Member postings for Ajohnw

This thread has gone a long way from Astromediashop goodies which is a pity really - not that they sell that much astro stuff really.

However people might find Michael's link rather interesting if they can find details in it concerning importing antiques. What I have found the past concerning HMRC's doc's though is that they are seldom complete and specific details may be hard to find.

Antiques - seems to be a good example of what may apply to one sector of society but wont to another.

I imported a 150 year old pocket watch from the USA once to restore. No chance of finishing until I have a furnace to make a new dial.

John

-

I've never been charged VAT on postage but have been charged more than £8 for admin. They should charge on postage so no idea why they don't always do that. Import duty is also possible on top of the vat, in fact I think it's added before vat when it has to be paid.

All stupid really. I asked a postman about it once. It seems that they get a lot in that has zero put in the customs value. However there is some indication that certain items are spotted when they go through customs and charged accordingly. Personally I don't mind the VAT but the £8 or more at times for sitting at my PC and paying the import duty and the £8 via a card electronically what ever it's value is really annoys me. It's all very treasure island Britain like many other sales related areas.

Then there are all of the parcels that come in from China that have $10 on them what ever is in it.

John

-

I must get a life . Just measured one. 50mm and focal length could well be 184mm. I measured it at 182. The lens cells screw on for focusing and has a locking ring. The baffle is approx 96mm back from the mid point of the lens and has 1" hole in it that might be 25mm. The hole edges should be very thin.

The baffle is very probably in the same place for right angle finders. It should be possible to scale the sizes for bigger lenses with longer focal lengths.

Somewhere to start anyway.

One other thing I can add. The size of the image the eyepiece views is 15 maybe 16mm dia.

John

-

Edited By Ajohnw on 18/01/2016 20:35:24

That's what life should be about Neil most of the time when it's possible - fun.

If you make the reflector you could be the only person around with a quartz over coated mirror.

One thing to note on finders. I have had several and all of the ones that are any good and don't show any chromatic effect have a baffle well down the tube with a hole in it. I think it does 2 things. Reduced the field of view and also and probably a lot more importantly increases the F ratio number - the entire lens will  still contribute to the image. The magnification calc is still the same as it always is, I'd base that around what 50mm finders usually offer which I think is around 8 or 9x

I might be teaching my grandma to suck eggs but just in case. I'll measure one up if you come to grief if you like.

John

-

Edited By Ajohnw on 18/01/2016 19:24:26

I have to sleeve 2MT draw bar thread fittings down to 5/16 bsw ega so I like the the thread in them to be a big as possible.

As the miller came I also have to use a spanner to tighten it - just a 5/16 bsw nut. The gain from the taper and thread means that this only has to nipped up. No need to tighten firmly at all.

In terms of what is needed when tightening think about the "enormous" sic. amount for force needed when a drill chuck is fitted into the tailstock even when it's being used to drill a 25mm hole. Well open it out from say 10mm or so anyway. I have more problems with so called self tightening chucks not doing so.

John

-

You could probably make something that expands in the spindle bore to add a release mechanism but I'm still inclined to think the OP is worrying too much about the simple way of doing it.

The trouble with adding a plate with a slot in it to the back of the headstock is the probable need to drill hole etc in it.

John

-

I've used Surplus Shed several times Michael. One trick which believe it or not can save money is to ask them to ship things separately. That sometimes results in all being below the import limit so no vat and better still no tax collection fee - that can vary a lot at times. Not sure why.

I understand the limit is now £15. It was £18 and had been for a long time so really aught to be £30 plus.

Last time I ordered off them was the optics for a Bath interferometer. Easily the cheapest for the items needed but also a small surplus Edmond's lens of Ebay.com. That can often also be a cheap source of optics,

Why a Bath - final check on a telescope mirror when I get round to actually making it.

I'd be more interested to know if any one else will be ordering the kit.

John

-

Edited By Ajohnw on 18/01/2016 16:46:03

I wondered about the cardboard steam engine. Maybe next time. Steam's separated from the cardboard from a quick read.

I have built the spectroscope kit as a trial for that particular type and to check some design maths out. I had the bright idea of using super glue. Fine if things are pressed down in exactly the right position. It would have been better to use something that could be unstuck and maybe leaving a bit of space for something stronger if needed later.

Immediate thoughts was Super Pritt but which now seems to be called Power Pritt.

They are the only source I know of for cheap achromats and the large ones were probably destined for finders.

John

-

One of the problems with digital things is that they usually have an error of +/- 1 of what ever their finest division is as what ever it is measuring may be nearly reaching it. Doesn't matter what it is even digital scales have this feature. The only one that doesn't as far I know are the ones Bwelectronics make. They resolve to more precision than they display. Most things don't 'cause it's good for marketing. Best example is mic's reading to a micron. If only the frames were rigid enough and ratchets etc or fingers consistent enough to do that. Actually people that use mic's a lot are usually aware that the ratchets even on analogue mic's are pretty useless - in the real world for instance more pressure is needed on flat surfaces than on diameters.

Analogue measuring devices can be gauged by eye against the scales, even on vernier scales to a certain extent.

The rest on both types comes down to how accurately they are made and ease of use for the accuracy that is needed. That is one area where I feel callipers fall down and aren't really suitable in many situations for super accurate measurements - not even to the accuracy that their readings suggest let alone the errors.

John

-

I wanted a lens for something and with postage costs just had to buy something else so went for this

**LINK**

Which will need translating. The kit can be bought from their UK agents

**LINK**

I will be interested to see if it does run backwards stood on a cold can of beer,

Some astro people might find the site interesting. eg Want a 450mm fl guide scope, no idea if it would work out. Or fancy a 60 or 70mm finder but don't fancy the cost. As with finders these lenses will probably need a stop in the tube to restrict the field of view.

I should add given how they have to pack some of the things they sell their postage costs are very reasonable.

John

-

I don't see the problem. If a collet or what ever has a locking taper unscrew draw bar a bit and tap the end of it. It can take a pretty hefty tap.

I did think of making a screw extractor for my dore westbury but it's not worth the effort. It doesn't cause any problems because the very end that I "tap" isn't threaded and the draw bar is located well in the spindle so can't flex much or anything like that. It should be easy to arrange for the same thing to happen in a lathe spindle. Assuming that the draw bar is much smaller than the bore of the spindle make a "nut" with an extension on it that is a nice fit into the spindle and say 1 bore diameter or more long. The thread on the draw bar itself could always remain in the "nut" so no worry about bending it or damaging it.

That sort of arrangement could be turned into a screwed extractor. It needs a fixed part that engages with a shoulder and pushes in the right direction when the "nut" is unscrewed. As there is usually no or little spare space on the end of a lathe spindle the fixed part could be a suitably sized clearance slot in a plate fastened to the headstock.

All a lot of effort compared with an arrangement that can be given a bit of a whack.

A "nut" that engages into the bore of the spindle isn't a bad idea when a draw bar is used to pull work back onto a face plate. It will help keep the draw bar central and on axis. If the draw bar is at an angle it can centralise it's self while turning the part and as a result woirk loose.

John

-

Edited By Ajohnw on 17/01/2016 17:36:46

Edited By Ajohnw on 17/01/2016 17:37:09

The reason people buy them is for the specification shown here which applies over the full range.

**LINK**

Mine hasn't got the data output. Cost around £85. I've had it over 3 years and changed the battery recently because I thought I may as well do it and was changing the battery in a Draper mic I bought.

My previous pair still work but the battery hatch has miss behaved at times and I wanted more than 6" of measurement range. I've had that one so long that I haven't a clue when I bought it. Sad the battery hatch is acting up because I doubt if I changed it more than 3 or 4 times and must have been a bit ham fisted once. The Mitutoyo hatch is more robust.

Actually for some reason I think the batteries don't fit properly any more it came with a spare and that and the one in it lasted a very very long time.

John

-

I bought some digital mic's over time a while ago Mitotoyo and M&W mainly because I thought I should. The Mitotoyo were significantly discounted. M&W full price, I couldn't find the same size in Mito at the right price. I recently replaced the M&W one with another Mitotoyo and advertised it on here. As far as I can check them all are fine. The last one I bought did come from a dubious source - ebay USA look what I have type thing and several of them. They went quickly. The battery was flat. This is one reason why they sometimes come up well below list price - same with a crazy Draper one I mentioned a while ago that I think some bought - I needed a mic of that size anyway.

My very 1st digital calliper came from an offers list that used to come through the post now and again. It lasted for many years and was very accurate but eventually the battery compartment started acting up even though they lasted a couple of years. Not being entirely happy with 6" I went for a mitutoyo 8". That was seriously discounted and just as accurate as the previous unbranded one. That one cost me £30, a lot when I bought it. At the time a very exotic item. It took months and months to arrive. Guess they obtained orders and then had them made. I'd guess accounting for inflation the Mitotoyo was cheaper.

Personally I think that it's best to have a sensible attitude about bargain prices. Part if too cheap and part exactly who is selling it. Works for me anyway.

What do I use most though - my 0-1 and 1-2 from training days both with verniers and a 2-3 but at this size there's not much difference between using a cumbersome digital mic and an ordinary one. I don't use my Kanon vernier caliper as I know both of the digital ones are as good. I also have a rather tarnished 30" vernier one, Super cheap and i have even used it a couple of times.

John

-

If you use the flash player it might be worth checking to see what version you have. There is one that has a security problem. This seems to be firefox related but may only relate to some OS's as Adobe haven't updated it for all of them yet and might not ever again. Seems Chrome has got round this by producing PepperFlashPlayer. This might just be a linux problem but the culprit player was used on all platforms.

I've been having a busy security time - some one pretending to be me in a chat window in a browser somewhere.

I've been using Chromium for a while. AKA Chrome but not by Google, it's just what Chrome was based on.

My favourite is Opera. Mainly for the way it handles bookmarks but an upgrade is way over due for me. Looks like I need to update my OS to get an update.

John

-

I'm surprised anyone parts off fully with the centre in. The clearance between the tool and work is very very low when the tool is cutting. When the part does part off - oh dear, the work tilts and as result reduces the clearance. A good way of getting a mangled end. It's best to let parts fall away unhindered really.

Afraid I use my hand if needed but best to remember that parts can be very hot so sometimes use something to catch it on the bed. It's usually the smaller bits that get hot.

On Myford 7 series lathes people often seem to find that a rear parting off tool works best. It depends on the particular lathe to some extent. I managed without on an ML7 I had but had to be rather careful about the feed rate. Too slow and lots of chatter and once it started the only way to get rid of it was a short sharp increase in feed rate and then back to something faster than I was using.

John

-

Edited By Ajohnw on 14/01/2016 12:34:10

Having a couple of sizes of these about Brian saves buying spanners of specific sizes.

Ebay 111839246996

That's what I use for things like slitting saws and a number of other things.

John

-

I've never looked at this but suspect that the logging in is retained in a cookie type thing and these have a life time set when they are stored on peoples machines.

As they sometimes last for a couple of days there must be something odd about the software that calc's the life time. Going on other forums they can clearly be set to last for an extremely long time. I'd say for ever going on some forums I am in.

John

-

I think you will find that the drying time is very lengthy when white spirit is used. So slow that it can help brush painting using a fairly thick coat. The brush marks will flow out but it's likely to take days to fully dry.

Thickness of the coat and the dilution is best determined by trying it. To much and it will run too easily.

5 to 10% water added to water based paints has a similar effect especially on timber but it dries a lot more quickly.

John

-

I think it's the forum. I always tick stay logged in but unlike other forums it doesn't work. Sometimes I stay logged in for a couple of days but often for just one day of late.

John

-

Personally I would put the O ring in a groove in the cap. So make the bottom, add bit of a chamfer to the inside edge of the top, polish and then make the cap. Aim for around 10% compression on the O ring but fit it in the groove and then try the base on it. Adjust accordingly while it's still on the lathe. This would mean that the total height of the top would have to be less than the depth of the cup - or it would be as I would make it.

I have a small spirit burner that has a ground glass cap to go with it. Trouble is that when it's filled with meths and left for a while the stuff still evaporates so I would make a cap for the burner as well. In that case it may be best to put the O ring in a groove in the cap then fit that to the top part again while it's still in the lathe. Polishing it in the area the O ring slides over.

The other way of course is to trap the O ring between surfaces and try some screw cutting. Aluminium isn't the best choice for that. It helps if it's anodised but it can still bind.

John

-