NEEAG May meeting

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Jol Wilkinson
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NEEAG May meeting

Postby Jol Wilkinson » Thu May 24, 2018 4:56 pm

NEEAG's May meeting will be held on Thursday, 31st May, at 7:00 in the usual venue:

The Colchester Society of Model and Experimental Engineers Clubhouse
13a President Road
Colchester
CO3 9ED

Activities will include further work on the groups Lavenham project and a "show and tell" session on members individual modelling activities, fuelled by the usual consumption of beverages and comestibles.

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Jol Wilkinson
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Re: NEEAG May meeting

Postby Jol Wilkinson » Sun Jun 03, 2018 1:12 pm

Eight members attended and we had a jolly time.

Richard M demonstrated cutting hinge slots in etched brass coach sides using a Proxxon miniature milling machine.

Various aspects of the Lavenham project were discussed including invisible track feeds using cast brass chairs, etc. but no actual modelling done. However, we are having another working day on Monday 11th June, so should make some more progress.

andrewnummelin
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Re: NEEAG May meeting

Postby andrewnummelin » Tue Jun 05, 2018 7:37 am

Jol Wilkinson wrote:...

Richard M demonstrated cutting hinge slots in etched brass coach sides using a Proxxon miniature milling machine.
...

I’d be very interested to learn more about this technique and wonder whether it would work with the thicker Trevor Charlton etches or with polystyrene. The smallest cutter I’ve tried using on my mill WAS a 1mm one, much too thick for hinge slots.
Regards,

Andrew Nummelin

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Jol Wilkinson
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Re: NEEAG May meeting

Postby Jol Wilkinson » Wed Jun 06, 2018 10:19 am

I'll ask Richard to explain it.

richardvmcl
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Re: NEEAG May meeting

Postby richardvmcl » Thu Jun 28, 2018 10:32 am

A short note on cutting 4mm scale hinge slots.

10 years or so ago I had an idea that a portal milling machine would be handy for making lots of parts in sheet brass. They are pretty popular in Germany and Austria for other modellers such as cutting lots of wing sections for wooden aeroplanes. I couldn't see how I could do the same for thin brass, especially how do you hold the thin metal sheet firm and flat - so went to some exhibitions and asked. The answer was simple - use a sheet of MDF as a substrate and nail or screw the sheet to it. When it gets chewed up too much, throw it away and get another piece.

I haven't yet followed up on the portal milling, but used a version of the same idea on my Proxxon micro miller to machine shapes in brass (and nickel and other) sheet.

Firstly I found a scrap of MDF about the right size to cover the X-Y table top, and attached with bolts and the T slots in the table. - picture 1. I made sure that I could remove it and re-fit accurately.
Secondly I attached a gate at the back as straight as possible and then ran a cutter along it to make it dead square.
Thirdly i put 2 threaded inserts into the MDF so that I could use machine screws for clamps. Neither the clamps nor the locations of the fixing locations are perfect, but they work well enough for me not to improve them.

With this I can clamp a coach side square to the X-Y table and nice and tightly.

From my foray into portal millers, I discovered that it was easy to buy conventional fluted cutters on an 1/8 inch shaft down to 0.4 mm from Sorotec in Germany, and plenty of other suppliers. My first efforts were with an 0.5 cutter, but they are extremely delicate and break much too easily. Don't copy me. The next attempt was a 'nice' fluted 30 degree engraving cutter which worked for many coaches but I thought that a finer angle was worth a try. My latest cutter is a 20 degree engraving cutter with a D cross section - I got a box of 10 of them for under £10 from China on Ebay. They offered various angles, and also with flat (such as 0.2mm dia) tips. I bought the pointed sort but I doubt that using 0.2 flat end would make any difference. This is the strongest, simplest and cheapest type of cutter. They just work.

The whole process is greatly helped by the Proxxon miller having no discernible backlash on any of the 3 axes. I keep it for really light and precise work.

When you look at etched slots in half-etch brass, most over-etch. With a tapered cutter, the width of the slot depends how deeply you lower the cutter - practice on a bit of scrap to get the width that you like. Cutting a slot about 0.5mm wide and about 1.2 mm long does leave slightly sloping sides (10 degrees off the vertical) but in something 5 thou thick it is not measurable and the end result is more precise than in almost all etched kits. Any gaps fill with solder anyway.

There is no reason for it not to work with Trevor Charlton sides and equally with polystyrene, though probably both with lower spindle speeds. For me it works fine at around 10K rpm with half etch brass and equally well at 20K (the top speed on the Proxxon). Polystyrene may need a lower speed to cut rather than melt. The Trevor Charlton sides that I have have pre-formed tumblehome so will need a shaped packing piece to clamp them properly.

Not a lot of magic. Once you have a source of cutters, the key is to really clamp the workpiece firmly and precisely, and don't rush. Each slot only takes a few seconds.
Attachments
Milling 2.jpg
Milling 1.jpg

andrewnummelin
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Re: NEEAG May meeting

Postby andrewnummelin » Fri Jun 29, 2018 1:30 pm

Richard,

Many thanks. Very clearly explained: I'll be ordering some of the bits and giving the technique a try on on my next project using my Sherline mill - unfortunately this does have a bit of backlash so some extra care will be needed.
Regards,

Andrew Nummelin


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