Member postings for Andy_G

Interesting project

From practical experience, I think that 2.6 HP would be way, more than required for a relatively slim hull:

A 2.2 HP petrol outboard would push our big, fat, inflatable dinghy with 3 people on board at more than walking pace on tick-over (this was an issue, as it didn't have a neutral!). At full throttle with one person on board, the thing could plane.

Rowing the same boat was a dismal experience - far less forward progress than a lesser effort in a wooden dinghy.

I think the ~0.5HP is much more likely. (Hull speed is ~5 kts, it becomes an exercise in rapidly diminishing returns if you are trying to exceed this.)

I use the battery water from Halfords - it’s only a few £ for 5l.

There can be a lot of dirt in dehumidifier water, but it might still work OK.

Note that you don’t need to use sulphuric acid - sodiumbisulphate works just as well, is easier to get hold of and less dangerous to handle and have around.

(I’ve posted details on this forum previously, but they’re also here:

**LINK** )

Edited By Andy_G on 21/05/2021 09:00:02

That looks like a hot rolled mill finish -

I've got some stainless strip here that looks the same (one of the 400 grades, I think):

I suspect it's hot rolled & descaled, but don't know for sure. I've seen full (~2m x 1m) plates with the same finish.

There are several finish options - I would guess this is 1D or 1E

It's still the right answer though.

I turned some 3mm diameter x 20mm long stainless ones by turning the blank down in stages (roughly 1/3 of the length at a time) then taking a very light skim over the stem to blend the sections together, but 1.5mm probably won't stand for that.

Joe Pieczynski's approach may be of interest (one deep cut, right to finished diameter):

Thank you!

I was pleased with it - TIG is very satisfying when it goes well (and equally frustrating when it doesn’t!).

100mm diameter x 2mm thick aluminium x 2 pieces on a Chinese 7 x 14 lathe the other week:

The disks were cut roughly to shape with a jigsaw first, and the protective film was still on the sheet which I think helped with drive. No problems encountered, I would use a bigger backplate next time (this was just a scrap of 40mm bar that I had to hand, I think. )

They came out very well IMHO:

Good enough for my welding, anyway!

Edited By Andy_G on 25/03/2021 00:17:33

I have a 12V motor from a child's ride-on toy (they eventually stopped crying )  that I think is well suited to this application.

It's about 105 mm long x 65 mm diameter and runs at ~3000 RPM on 12 volts. It's capable of drawing huge currents (10A+) but I have it running on a 3A speed controller which is sufficient to put a 6mm drill through mild steel quite easily and run small milling cutters.

It runs through a belt drive to an ER11 spindle (running in angular contact bearings) that gears this down slightly (~1.5:1) which I use mostly. I also have a larger motor pulley and a longer belt that fit the same centres that allow the motor speed to be geared up by 2.5:1 if needed. (I seldom use this though, as it isn't fast enough for a grinder, and the slower speed works fine with every size of drill that I've used (6mm down to 0.7mm).

The only drawback of the pulley arrangement is that I need to flip it to the opposite side when I change from cross drilling to face drilling as there isn't enough travel on the cross slide of the mini lathe to be able to accommodate both positions on the same side of the toolpost.

Edited By Andy_G on 18/03/2021 18:31:20

I think he has previously mentioned 20HP - as above, I don’t think he’s factored in the racing model engines, but good luck to him anyway.

Just double-checking that this is the design being discussed:

http://www.modelenginenews.org/etw/roller/page52.html

To correct my spring numbers above - It's 1/4" OD, so the relevant stiffness figures are 0.07 - 0.12 lb/in

(If the scale factor is 1.4, I think the spring wire should be about 0.015" dia ).

Have you run it long enough for it to warm up? (Not unusual to have to lean out the mixture considerably over the first minute, or so.)

What happens if you open the throttle? (I presume you mean the spring loaded sleeve when you say 'air slide ' ) - Apologies if I have got the wrong end of the stick.

Edit to remove random smiley - have just seen latest info.

What size of primary choke are you using? (The hole in the side of the carb)

If the primary choke is too big, or there isn't a good seal between the air sleeve and its cylinder, the carb won't develop enough vacuum to draw the fuel through. Might be worth trying with a bit less than 2" height difference.

Edited By Andy_G on 01/03/2021 18:17:54

Could it be that the spring is too soft? (i.e. the air sleeve is massively over-shooting the desired setting, causing oscillation). If I read the original article correctly, it suggests a spring of 12 to 20 turns 1/2" OD 32SWG which I've calculated as 0.008-0.014 lbs/inch. If the design has been scaled up, the starting point would be these stiffness values multiplied by the square of the scaling factor. (Simply scaling the spring diameter up will result in a softer spring).

I would expect a damper would undoubtedly help though.

Edited By Andy_G on 28/02/2021 13:43:44

There are photos of a 'CD 210V' change gear setup on various ebay listings (whether it is the *same* CD-210V or not, I don't know:

Listing is here if the picture doesn't work:

https://www.ebay.co.uk/itm/UK-CD-210V-MINI-Lathe-Machine-Tool-Woodworking-Table-Metal-Gear-750W-Spindle-CE-/154105712191

Not sure if it's a date thing, or a location thing, but all the belts hung up in the back of the barn on my grandfather's farm in West Wales were canvas. (There were about half a dozen: about 8" wide and rolled up into a coil about 3' across.) These would have last seen use in the 1940s or 1950s - my mum was born in the 1940s and remembers the threshing machine coming to the farm.

In the 1970s he still used flat belts to drive a feed mill and a terrifying circular saw from the tractor. These belts were also canvas with metal 'claw' joiners. The belts were dressed on the inside face with what looked like an oversized lipstick - the outer case was about the size of a 'Smarties' tubs and made of orange cardboard.

Edited By Andy_G on 21/02/2021 14:25:39

I came across somebody making them from book-binding tape a while ago - seems to give a reasonable scale appearance (even better in a tan colour IMHO):

Yeah, I suspected something as such.

I was seeking to address the "may not be appropriate to a small scale model" concern

My little horizontal engine is designed with 4:1 compression ratio, and runs quite happily with noticeable compression/bounce when flipped over (~21mm bore).

Leaky valves seem a likely suspect.

Does it start: "Batman....?"

That’s the way I would propose to do it. It’s the way I made my one and only single cylinder IC engine crank shaft. (Steel crank webs silver soldered to silver steel shaft & crank pin).

I await more learned comments with interest.

Sorry - I thought you were referring to an engine design (My fault!). I'm guessing it is the same one as in the Seal construction article - Link and also the type used in the video above.

Yes, two 45 degree helical gears of the same hand will mesh at 90 degrees with crossed axes. However, 45 degrees is something of a special case as both gears in the pair have the same helix angle. Otherwise, the helix angles just need to sum to 90degrees - think of a worm wheel as a single tooth helical gear with a >85 degree helix angle.

I'm guessing that the 21.5 degree helical gears are intended to mesh on parallel axes (as per spur gears) in left and right handed pairs. If one wished to create a 90 degree drive with these, the matching gear would need to have a helix angle of 68.5 degrees (90-21.5 if I've done my maths correctly).

I suspect that the reason that only 45 degree skew gears / crossed helical gears are readily available is that the number of other variants would be huge otherwise.

From the above, it sounds like you are more comfortable with DP than module. I'm the opposite, but will try an example:

Pitch diameter of a spur gear is [#teeth]/[DP]

=> 60 tooth 40DP spur gear has 1.5" PCD

Pitch diameter of a helical gear is [#teeth]/([DP] x [Cos(b)]) where b is the helix angle.

=> 60 tooth 40DP 30 degree helical gear has 1.732" PCD

=> 30 tooth 40DP 60 degree helical gear has 1.5" PCD

Note that [DP] corresponds to the pitch *normal* to the tooth - i.e. on a plane rotated by angle (b) wrt the gear axis. The tooth outline looking down the axis of the gear will not be the same as a 40DP profile (although there is a way of specifying helical gears by this profile, the normal DP (or module) still needs to match for them to mesh).

If you play with the angles in the 30+60 degree example, you can see that the centre to centre spacing of the pair (sum of PCD/2) can be varied while keeping the same gear ratio and normal DP.

The contact between the gear teeth is largely sliding so they aren't ideal for transmitting high loads.

I hope I haven't further confused you!