Carburretor Thoughts

[Art K]

Roger,
Could you turn the tapered portion between centers then cut the end off, leaving the tapered portion.
Art

[Jo]

The old trick for carb needles is to repurpose sewing needles. There are various types of sewing needle and sizes to choose from you should find something suitable.

If you wish to 'turn' one then you are in the watchmaker's turning domain: Supporting the needle in a groove or hole in a jacot tool from the tailstock then using a very fine needle file and a burnishing tool to hand shape the point. I'll see if I can find the details of how to do this    ...

Jo

[Jasonb]

If you don't want the bother of making or buying jacot tools then a piece of wood or MDF with a Vee filed into it held in th etool post will support the work while you file and then stone the taper. If you look at Ramon's builds you will see him doing this which is where I got the method from. Though most of mine are just turned on the chinese "watchmakers" machine

[Roger B]

Thank you all for your interest and suggestions   

This was a first attempt to see what I could do the 'easy' way. I have similar issues grinding the injector needles for my fuel injection system and noted there that I need an additional support.

A point on the end of the needle is no problem so possibly a small inverted centre would work. If I can taper the outside down to 0.5mm diameter it won't interfere with the lathe tool. Another option is form of fixed steady mounted on the saddle again possibly with a spring loaded inverted centre.

These needles with have a defined profile so they will need to be turned or ground (I also need to add a DTI to the cross slide).

[Jo]

  That support looks familiar.

Jo

[nj111]

You seem to be making some good progress. For ease of adjustment I recall needles need to have a finer taper than those we are used to seeing on glow engine carbs. As glow fuel is run around air /fuel ratio 8:1 (?) and of course petrol nearer to 15:1

[Roger B]

That support looks familiar.

Jo

    

[Roger B]

I made some pivot pins for the jet adjuster and then made a jet. I started the hole with an extended 0.5 mm drill from my fuel injection work and then finished with a 0.8mm drill which I assume will be oversize.

Next step was to make a tailstock inverse centre and try another needle. The concept worked but I need to reduce the size of the centre so I can get the end of the needle to 0.5-0.6mm.

[awake]

That is some fine work - and yes, pun intended. Fine in every sense of the word!

[Roger B]

Thank you 

I thinned down the inverse centre and had another attempt. I let this be oversize to check the actual jet bore. It appears to be around 0.83mm so I will have to design the real needle around that. The needle seems to have a similar taper to the first one so deflection may not be the problem. The inverse centre certainly allows bigger cuts. I check my precision cheap angle gauge and zero is not zero  Time to spend money on something better 

[crueby]

I remember buying a large square at the hardware store for woodworking projects. As warned by a friend ahead of time, I checked them in the store - one edge against the side of the shelf to my right with second side across the shelf - light pencil line, then flopped the square over so the first edge was over on the left, looked at the line again against the second edge.... went through the bin till I found one that actually WAS square! Amazing how far off some of them were.

[Roger B]

I have a better angle gauge on order and thought I should also check my collection of squares. They were not as bad as expected being cheap imports, but one had a tapered blade. The inside 90° was almost spot on, the outside was way out, ~0.5mm in 70mm.

Getting materials is starting to be a problem    I had identified a suitable piston spring from Lee Springs but they won't supply to private customers at present. I asked in the toolroom and work and they suggested a Swiss supplier who also had something possibly suitable but they also won't supply to private customers  In this case I can order through work but it will take a little time. I found a supplier of small fasteners in the French part of Switzerland who appear to be able to supply some of the small screws I need, especially some M1.6 x 2mm grub screws to hold the needle in place. I wait and see.

As I can't move on with the carb at the moment I went back to the fuel pump and started on the valves. The Regner unions I usually use have a bore of 2.5mm which is a bit large for the seating of a 3mm ball so I made a copy with the bore reamed 2mm. The seat was finished with a 3.2mm drill ground flat. A quick suck test showed a good seal without tapping the ball to get a seat. I then pilot drilled the ports in the body and milled flats for the valves to seal on.

[Roger B]

As I was in milling mode I moved onto the ball and socket for the diaphragm rod of the pump. The seat was cut with a 3mm radius end mill and the form tool was roughed out of key steel with same cutter. I filed some clearance and then heated to dull read and quenched it. The ball was cut from 6mm hex and taped M2.

The next step was to finish the valve seats in the pump body. The inlet was just drilled 4.5mm and tapped M5 x 0.5 as the seat is in the union. The outlet was reamed 2mm and the seating was cut with a 4mm end mill.

[Roger B]

I received my new protractor which is somewhat better than the old one. It has an additional arm that can be fitted for measuring dovetails and similar. I found that with careful adjustment I could measure the needle directly 

I finished off the pump arm's various holes and slots and will then move onto the rest of the piston rod parts.

[Roger B]

The clamps for the diaphragm were made from 6mm brass rod and tapped M2 and parted off to 2mm long. The piston rod is 2mm diameter stainless steel threaded M2 both ends. I put it together with some M2 bolts as temporary piviots to make sure nothing jammed.

<a href="https://www.youtube.com/watch?v=65RV1i12yf4" target="_blank">http://www.youtube.com/watch?v=65RV1i12yf4</a>

Next up is a bracket to fit it on the Proxxon lathe for trials as if driven by a camshaft I can expect 3-4000 rpm. This is just hacksaw and file work on a piece of 30mm aluminium angle.