Two Stroke Reed Valve Material

[Peter Twissell]

What does anyone use to make model size reed valves?
I need to make valves about twice the size of those found in Cox .049 engines, which I think are made in both steel and Mylar.
The Cox valves operate slightly differently to conventional reeds - they are not fixed at any point, but are allowed to float between the port face and a retaining clip.
I need to make petal type valves, about 9/16" (14mm) diameter, fixed in the centre and with 4 petals.

Any ideas?

Thanks,
Pete.

 

[GailInNM]

I did something similar about 15 years ago for a couple of1.6 cc engines I built.. I used PTFE,, about 0.004 or 0.005 thick as I recall.
I cut them out using a laser engraver and did several different thicknesses and all worked fine. The PTFE sheet I had was on a roll so had a slight curve in it so I put it between two sheets of aluminum and baked it in the domestic oven at about 450 deg F for a couple of hours. No clamping, just the weight of the alum sheets.
PTFE is easy to cut by hand using a hobby knife with out raising a burr making an alum template to cut around may be useful.
If cutting with a laser, use lots of power so the PTME is ablated and not melted. This will give you a burr free edge and also avoid generating any toxic fumes.
Gail

 

[Peter Twissell]

Thanks Gail!
PTFE is on my list of possible materials.
I was not sure whether it would be stable enough. I have used it in other applications and found that it 'creeps' over time.
I expect it is constant load which leads to the creep and a reed valve never sees constant load.

 

[Nerd1000]

Could you use thin steel shim stock? A lot of reeds in full sized engines seem to be made from thin metal sheet.

 

[Peter Twissell]

I could of course use steel, but need to cut it to shape while keeping it perfectly flat. Etching perhaps?

 

[aka9950202]

I could of course use steel, but need to cut it to shape while keeping it perfectly flat. Etching perhaps?

Do you have access to a laser cnc machine or someone who has one?

I built a cnc router machine and am considering adding a laser to it. I know there are 3d printer/cnc router, engravers / laser cutting machines ideal for hobby use.

Cheers,

Andrew in Melbourne

 

[stanstocker]

I could of course use steel, but need to cut it to shape while keeping it perfectly flat. Etching perhaps?

Greetings,
I've had good results when making small thin brass objects using super glue to secure the work to a fly cut sacrificial substrate / pallet. Then proceed to mill. In my case it was to make annex springs for Chelsea Ships Bell clocks. These are basically a single ended leaf spring, around 40 thou (1mm) wide, and 1 inch (25mm) long, and with a tab on one side that gets two #72 holds for the holding screws. The spring region of the profiled part is burnished to work harden and provide good action then the entire pallet is plopped in acetone overnight to dissolve the super glue. The tab is folded 90 degrees, just to add some fun and force discipline in not burnishing too close to the fold line. The brass shim stock was 10 thou thick stuff IIRC, it's been years since I last made these. I needed these just often enough that I set it up on my baby CNC mill and knocked out around a dozen / lifetimes supply one day. Pretty sure a 1mm end mill was the cutter of choice.

Cheers,
Stan

 

[stanstocker]

Do you have access to a laser cnc machine or someone who has one?

I built a cnc router machine and am considering adding a laser to it. I know there are 3d printer/cnc router, engravers / laser cutting machines ideal for hobby use.

Cheers,

Andrew in Melbourne

Hi Andrew,
The small diode lasers / up to 120 watt CO2 lasers we mere mortals might have in home shops won't cut steel or other metals sadly. Fiber lasers are coming down in price steadily, perhaps one powerful enough to deeply mark / engrave thinner steels will have the power to cut thinner materials.

There are marking coatings that can be applied to metals that allow a lower power laser to permanently mark the metal, some folks just use yellow mustard with good results

I am very happy with my 10W double diode laser for dicing up 5 mm and thinner ply and wood or card stock, not saying they aren't wonderful tools, just not for metal.
Cheers,
Stan

 

[Nikhil Bhale]

You can check reed valves from AC compressors (big industrial types).
Maybe they are of the size you need.

Regards
Nikhil

 

[Peter Twissell]

Thanks for all the suggestions.
I am quite familiar with steel shims from my many years in shock absorber design and manufacture.
If I were to go for steel, the parts would be etched, deburred and polished in the same way as shock absorber shims.
At this scale, I am leaning more towards Mylar or a composite material with lower mass and stiffness and better surface conformity than steel.

 

[Chiptosser]

The metal reed valves used in most engines before composites where made from spring steel. Shim stock tends to fatigue and break at the flex point.

 

[Peter Twissell]

The "shim" to which I refer is a specific spring steel developed for use in shock absorbers. It's very resistant to fatigue, but I can't get it in less than 0.1mm (4 thou) thickness.

 

[Gary C]

I think all early Cox reeds were beryllium copper before they moved to Mylar. BC shim is still available.

 

[Peter Twissell]

The Cox reeds work a little differently to others. The reed is allowed to "float" over the port with it's lift limited by a wire clip. It doesn't need to bend to open the port.
My design must be fixed at the centre to keep the petals aligned with the port openings.

 

[bluejets]

My design must be fixed at the centre to keep the petals aligned with the port openings.

Cheat is to keep your eye open around scrap dealers for old whipper snippers.
Many have reeds that can be used depending how you design the setup.
Stripped one out just the other day, nice and "miniature" and in like-new condition, housing the lot.

 

[Peter Twissell]

Ok, I'll bite...
What is a "whipper snipper"?

 

[bluejets]

Google it .........

 

[DaveJones]

Strimmer.
Actually quicker than writing Google it...............

Not sure if it's applicable for your intended use but I have cut reeds for Cox engines from phone screen protectors.

 

[Nerd1000]

Ok, I'll bite...
What is a "whipper snipper"?

A line trimmer or 'weed eater'.

Unfortunately they don't all have reeds, some are instead piston ported.

 

[Peter Twissell]

Yes, I have a strimmer engine and it's piston ported!
Enough speculation now, I've designed a rig for testing reeds - a simple piston pump using the reed for inlet and piston port outlet with a cheap anemometer to measure air flow rate.