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Old 2nd Jul 2015, 8:31 pm   #1
Station X
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Default Making a brass trim ring for an Ekco AD65. INTRO

Brown Ekco AD65 receivers have a "brass" coloured semi-circular trim ring which sits in the middle of the tuning scale. It's actually made from Mazak, a zinc based alloy, also known as "monkey metal" with a "brass" coating. Mazak is a very brittle material, so it's hardly surprising that many AD65's have a snapped ring. In my case, not only was the ring snapped, but a piece or pieces was missing too. This left me with no alternative apart from making a new one.

There are several ways of tackling this job, depending on the facilities available. This thread describes how I successfully produced a new ring.

The picture shows the remains of the broken ring, not the new one.
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Old 2nd Jul 2015, 8:43 pm   #2
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Default Re: Making a brass trim ring for an Ekco AD65. MILLING.

The first thing I needed was some brass bar of the correct trapezoid cross section. Measurements of the broken pieces showed that the height and bottom width were 1/4" and that the internal angles at the bottom corners were 75 degrees. I couldn't locate a commercial source of brass bar with this cross section, so I had to make my own from 1/4" square material.

I made up four clamps to hold the brass bar on the table of the milling machine at an angle of 15 degrees (90-75 degrees) to the cutter. By the time I'd finished I'd spent more time making up tooling than making the actual ring. It's a good thing this is just a hobby!

The clamps were fixed to the milling machine table and the bar material was clamped into them. I took several very light cuts using the power feed on the X axis. Light cuts are needed because the bar isn't continuously supported. I had to move the bar along and take a second set of cuts because the X movement is less than the length of bar required. I allowed extra length because pyramid type ring rollers won't bend the ends of the material. I'll call the extra length "extensions"

In case you're wondering, the old toothbrush is used to clean out the Tee Slots.
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Old 2nd Jul 2015, 9:29 pm   #3
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Default Re: Making a brass trim ring for an Ekco AD65. BENDING.

Having made some material of the correct cross section, the next thing to do was to bend it into a ring. I used a ring roller for this, but I had to make up some special rollers to support the trapezoid material firmly so that it didn't bend along the wrong axis. These rollers were made from two slices which made it easier to machine them to the correct cross section. The driven roller slices are clamped together and keyed to the shaft.

Achieving the correct radius was tricky. I rolled the material until its radius was slightly larger than the broken pieces. Then it was a matter of removing the embryo ring from the rollers, positioning it on the tuning scale to see how it fitted and the returning it to the rollers for rebending. The last bit is tricky as the material is springy. Apply too little pressure and it'll spring back. Too much pressure and the radius will be too small.
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Old 3rd Jul 2015, 9:38 pm   #4
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Default Re: Making a brass trim ring for an Ekco AD65. DRILLING AND TAPPING.

The next step was to drill and tap the ring for the screws which would be used to attach it to the tuning scale. The holes, although equally spaced, do not have the same spacings as those in original AD65 tuning scales. This was because I had mislaid my original heat distorted scale and couldn't measure the hole spacings. This didn't matter though as I have a new tuning scale without holes.

After careful marking out, the ring, still with its extensions attached, was clamped to an X-Y table on the drilling machine so that the holes could be accurately drilled. A centre drill was followed by a tapping size drill and the holes were then tapped 6BA.
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Old 3rd Jul 2015, 10:04 pm   #5
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Default Re: Making a brass trim ring for an Ekco AD65. MAKING HOLES IN THE TUNING SCALE.

I now had to make holes in the new tuning scale to match those in the trim ring.

Short lengths of sawn off 6BA screws were screwed into the trim ring with just enough protruding to enable them to be unscrewed. I then applied masking tape to the new tuning scale at the approximate positions of the holes.

The trim ring was then placed gently on the tuning scale and manoeuvred to the correct position. Once satisfied that the ring was in its correct position I applied firm thumb pressure to the ring at the screw positions. This left clear indentations in the masking tape marking the hole positions. This procedure was actually carried out with the ring extensions still in place, but I neglected to take a picture. What you see is a posed shot with the ring cut to its correct length.

The holes were made with a ring punch, as it is not safe to drill new tuning scales, they have a habit of curling up round the drill bit! The holes are slightly oversize for 6BA to allow for final adjustment.
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Old 4th Jul 2015, 9:53 pm   #6
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Default Re: Making a brass trim ring for an Ekco AD65. FIXING.

Having temporarily attached the trim ring to the tuning scale, the points at which the extensions were to be sawn off were marked. The extension pieces were then sawn off and the ends of the ring filed off at an angle to match the original. (No picture).

The final step was to polish out any scratches. I decided not to apply clear lacquer to the brass. Instead I'll let it tarnish naturally so it's a closer match to the original.

Oval washers were used under the heads of the fixing screws, as when backlit by the pointer, round washers would have shown up in silhouette.
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Old 4th Jul 2015, 10:19 pm   #7
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Default Re: Making a brass trim ring for an Ekco AD65. INTRO

That's outstanding work and a great writeup! The ring on mine is brown, and I'm not sure what it is made of. It may have been replaced when it was restored.

How long did the whole lot take to do by the way?
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Old 4th Jul 2015, 10:42 pm   #8
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Default Re: Making a brass trim ring for an Ekco AD65. INTRO

Quote:
Originally Posted by Station X View Post
Brown Ekco AD65 receivers have a "brass" coloured semi-circular trim ring
Actually they are brown painted mazak metal - sometimes seen unpainted as well, but I'm not sure if those rings were intentionally left plain or if the paint has been lost over the decades. The scaled down semi circular rings on the AC85 and AC86 models are similarly seen painted and plain mazak too.

However, you've done such a good job producing your brass ring I would suggest it looks perfectly fine as-is - really excellent work Graham!

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Old 5th Jul 2015, 10:21 am   #9
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Default Re: Making a brass trim ring for an Ekco AD65. INTRO

Marvellous! It's wonderful what can be achieved with a well equipped workshop, and of course the skills to make best use of it, which Graham clearly has. I'm very jealous. As he says, there's many ways of approaching the problem. This is my low-tech method, used to replace the ring on my AC76 purchased from forum member "Lowemission" a couple of years ago. He claimed to have dropped it, but it was clearly very distorted and wouldn't have gone back on the tuning scale anyway. The only machine tools my workshop contains are an electric drill, 6" engineers vice and a large hammer! So I needed to think carefully how I could produce a replacement. In all truth this a bodge, but it has turned out OK to the casual observer.

I wanted to retain the original tuning scale so I started by making a full size drawing of it and where all the fixing holes were. This showed that the scale itself had distorted over time, as one or two of the holes were not on an exact radius, being up to 2mm out. Combined with the distortion of the ring , this had resulted in some cracks around the fixing holes. I decided that I would attempt to produce a ring that fitted the existing scale with all its imperfections, rather than a geometrically accurate one that would put more pressure on the scale. This might have looked a bit odd when fitted back in the set but thankfully it looks OK.

So then I needed some raw material. Aluminium would be easy to bend but is a bit too soft for this sort of thing and is very unforgiving of errors. Brass would have been ideal, but I couldn't find any easily. I settled on mild steel 1/4" square bar from the local B&Q. The next thing to make was a template to bend around, fabricated from a piece of hardwood faced with some aluminium sheet. I had some idea that I could get the bar up to a cherry red temperature to make it easier to bend, but in the event my blowlamp was pathetically inadequate and all I achieved was a bit of charred wood. The next decision was to bend the bar before changing the cross-section. I thought it would be easier to bend and maintain some degree of flatness if it was square rather than with slopey sides.

And so to the bending. With one end of the bar firmly clamped in the vice it was not too difficult to get the approximate radius in place. It then took many slight "adjustments" along the bar to get it the right size and shape. The 1m length of the bar proved invaluable here in providing sufficient leverage. Having got a good approximation to the required curvature, I cut off the "extensions" ,as Graham calls them, to get the ring to the exact length. The next step was to add the trapezoidal cross-section by filing and finishing off with emery cloth. This proved reasonably straightforward. The final step was to add the fixing holes for the dial. These obviously must not go all the way through to the outer surface so need to be "blind" Drilling blind holes is OK, but I didn't think much of my chances to do blind-tapping successfully. I didn't have the taps, either. So I chickened out and used small round head self-tapping screws instead.
Painting the ring went reasonably well. I used several Humbrol model enamels mixed to the right shade of muddy brown. For some unknown reason this remained "tacky" for several days and so ended up in the oven for a good baking for an hour or two. Finally it was dulled down a bit with steel wool.

The overall result is not perfect but does the job. If I had to do it again I would make more of an attempt to get some brass bar which would make things slightly easier.
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Last edited by Dickie; 5th Jul 2015 at 10:42 am. Reason: typo.
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Old 5th Jul 2015, 2:31 pm   #10
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Default Re: Making a brass trim ring for an Ekco AD65. INTRO

I'm impressed with the nice clean machine tools Graham and the way you produced the final job.

Jim
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Old 13th Jul 2015, 6:45 pm   #11
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Default Re: Making a brass trim ring for an Ekco AD65. INTRO

Sorry for the delay in answering the questions raised by forum members.

After all these years I doubt anyone knows exactly what colour these bars were originally. Paint fades or wears off. Plating tarnishes or peels off. I rather like my natural brass bar, but I expect it will discolour and eventually look more the colour of a 1P or 2P coin.

The 1/4" square brass material came from an eBay seller. The difficult part is getting the length required. Sellers generally buy in the bar in lengths of several meters and cut it into 2 foot lengths for easy postage. Fortunately the long length I ordered didn't get damaged in transit.

I think the whole job including making tooling took about three four hour days spread over a couple of months. I always have several projects on the go at once and take frequent coffee breaks. Now I have the tooling I could probably make a ring in two or three hours. The difficult part is getting the correct radius.

My machine tools look clean because I cleaned them before starting work and this job didn't produce any swarf, just brass dust. By contrast, the suds trays on my lathe and small CNC milling machine are full of steel swarf.

Dickie. I like your approach, making best use of the facilities you have. Well done. I had considered bending my ring using a home constructed "pipe bender" arrangement. However I wasn't sure what radius to make the former to allow for the spring back. Also as I had pre-machined the brass to the trapezoid section the former and rollers would have had to match this. I'd bought the ring roller for another job, so elected to use it.
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Old 14th Jul 2015, 7:48 am   #12
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Default Re: Making a brass trim ring for an Ekco AD65. INTRO

Thanks Graham. "Needs must" y'know. The springback of the bending process was the only part I did not have under control.
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Old 17th Jul 2015, 10:17 am   #13
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Default Re: Making a brass trim ring for an Ekco AD65. INTRO

Great write up, both of you! Both methods require significant skill and patience, in rather different ways. I don't think I'd fancy my chances at filing a nice trapezoidal section on a straight length, let alone one already curved - and the result looks really excellent. Graham wins however if you want to make 50 of them

I'm into metal casting, and have been looking at the curly plastic trim on my Cossor 500 with a view to making an Ali replica. But...it's very thin and quite large, and the metal would almost certainly freeze part way round the mold unless I made it rather thicker than original. The subject of this thread however would lend itself to an attempt at casting. If either of you fancies PMing me a sketch, it would be very interesting to have a go some time - turning a 'plate pattern' in wood should be relatively easy given it is circular, though it might not fit on my 4.5" lathe.

There would be a good bit of clean-up by hand, so maybe such a method would resemble Dickie's more than Graham's.

(I can do bronze too, but then materials costs start to come into it. Then again, owners of such a prestige device might well want to invest in such luxury )

cheers
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Old 17th Jul 2015, 11:36 am   #14
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Default Re: Making a brass trim ring for an Ekco AD65. INTRO

Fantastic work, Graham. I was particularly impressed with the custom clamps for the bar work - they must have created a lot of steel swarf! Then to have to make custom rolls added to the pile. How often is it in our multi-skill hobby that more time is spent in making the tools for the job than in the actual job itself BUT that is a large part of the satisfaction in doing a job properly. Once again Graham, a really super writeup on making a very good replacement part.
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Old 17th Jul 2015, 12:05 pm   #15
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Default Re: Making a brass trim ring for an Ekco AD65. INTRO

mark in manc

I did consider casting a trim ring. What I planned to do was make a steel mould on my CNC milling machine then pour molten pot metal into it. The idea got shelved though because I had no 3D drawing package and no software to convert the drawing to the G Code needed by the machine.

I didn't actually make any drawings for the ring I made. I've described the cross section in previous posts. It's difficult to measure the diameter of the ring now it's installed, but it's about 11 7/8" OD.

I can send you the couple of sections of broken ring shown in post #1 if that would help.
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Old 17th Jul 2015, 8:24 pm   #16
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Default Re: Making a brass trim ring for an Ekco AD65. INTRO

Ahh...11 7/8 OD won't go on my lathe, though I could do it on one at work. You've described the section - I should have a go.

Have you ever tried to use your rollers to cold-roll a shape into (say) rectangular Ali bar? I have a lot of shallow D section to make, about 1/2" on the flat and 1/4" tall - much too long to cast - and I have been wondering how to do it.

cheers
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Old 19th Jul 2015, 10:11 pm   #17
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Default Re: Making a brass trim ring for an Ekco AD65. INTRO

Quote:
Originally Posted by mark_in_manc View Post
Have you ever tried to use your rollers to cold-roll a shape into (say) rectangular Ali bar? I have a lot of shallow D section to make, about 1/2" on the flat and 1/4" tall - much too long to cast - and I have been wondering how to do it.

cheers
Mark
Mark.

I don't think pyramid ring rollers would be suitable for rolling flat section into I__I section. For that you'd need rollers which were very close together with the male profile on one roller and the female profile on the other. Ring rollers can't do this. I think you'd also need three or four pairs of rollers geared or chained together. The first pair of rollers would simply guide the flat material and subsequent pairs would progressively roll the profile.

For the record I've successfully rolled 1/2" square bar into a ring using the rollers shown.
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Old 26th Aug 2015, 10:46 pm   #18
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Default Re: Making a brass trim ring for an Ekco AD65. INTRO

Graham, fantastic job mate, looks great, have you thought about selling any, I would be up for a couple let me know
Cheers and thanks for the detailed look
Graham Rowe
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