Member postings for Andy_G

Thank you very much - That's an impressive collection you've got there.

I don't believe my EGT readings: I think the TC was waving about in the breze a bit too much to be credible. I will drill the NGV / tailcone to hold the TC nearer the turbine exit to get a more trustworthy reading.

I want to get the EGT and a reliable RPM reading before I run it again. I've got a hall effect sensor working, but am waiting for a suitable magnet to arrive from China before I can try it out on the engine. The intention is then to measure the thrust and run it up to 100,000 RPM. (After that, it'll probably sit gathering dust !)

I did try and buy an Inconel disc - it's difficult stuff to get hold off. I was quoted £75 for a 15mm length of 2.75" dia 718 (+£18 carriage + VAT). - that was the shortest I could get. I did have the offer of a couple of slices of a 6xx Inconel, but after the donor had killed two bandsaw blades without making much progress on cutting the bar, the offer was politely withdrawn.

Thanks for the interest,

If there are any aspirations towards high performance, then a commercially cast inconel turbine is a necessity. Unfortunately, they are probably less available now that they were ~15-20 years ago, as the co-operative DIY efforts have morphed into commercial entities, and the supply of parts to hobby builders has dried up. (There is nothing available via the GTBA - I am a member.)

About the only non-Chinese source is Jetmax, as you say, but taxes and shipping pretty much double the advertised 230 euro cost of a 66mm turbine wheel (and you'd probably want the matching inconel NGV which would cost the same again.).

There are cast turbine wheels advertised on Alibaba and other Chinese sites which are about half the cost of the Jetmax ones.

In any case, I thought that was too much money to sink into a project for me (I didn't want a jet engine, particularly: I wanted to *try to build* a jet engine) - the Kamps design is one of the few still available that will tolerate a home made turbine (even a stainless one), albeit ar reduced performance, which is why I chose that design - I was very tempted to try one of the original FD3 variants (since this is what had sparked my interest, back in the 1990s) but the Kamps is a much better design.

If you just want a jet engine, the answer is to buy one! :D

There is a GTBA project engine coming to fruition that uses a radial inflow turbine (rather than an axial turbine as used in most of the model jet engines) that would allow turbocharger turbines to be used.

Thank you!

Yes, I did end up making a spot welder, after trying and failing to TIG everything - I didn’t follow any specific plans, just used a larger than usual microwave transformer (from a very old commercial microwave) and replaced the secondary with the heaviest cable I could fit in there. It’s controlled by a 555 timer IC and a solid state relay. It packs quite a punch and welds 0.5mm stainless in less than 0.1 seconds.

A little more info

Edited By Andy_G on 02/07/2022 22:59:59

Thank you!

The turbine wheel didn't take as long as I thought it would - it was split over several sessions, so it didn't seem too bad:

• Cutting the blank and turning the profile;
• Slitting the disc into blades;
• Putting the initial twist into the blades;
• Cleaning out between the blades and the initial shaping (with an angle grinder);
• The first go at smoothing and shaping the blades;
• Second go at shaping, and carving the concave faces with a dremel.

Each of those took an afternoon, pretty much (some afternoons were longer than others!)

More details of the process I followed here:

Turbine wheel blank

Forming the blades

I've made the tail cone, but it only appears in the first video - I want to confirm that the exit temperature is under control before running the engine up with it in place. I think that people who fly these things sometimes use an internal exhaust duct that they call the jet pipe - I don't have any plans to put this in a plane, so I haven't made one of them.

Thanks to all for the kind comments.

Thank you!

Inpired by comments on the 'See through Jet Engine' thread, here's my engine:

It's based on the plans in Thomas Kamps' book and eveything except the compressor wheel (a turbocharger part) was made in my shed on my Chinese 7x14 lathe.

The turbine wheel was hacked out of an Hastelloy X disc with an angle grinder and a Dremel, but came out well, I think:

There's a fairly detailed write-up of the build on my website

https://misterg.org.uk/turbine-html/

(Link)

First start-up

For the real massochists, an video of me mumbling as I assemble the parts:

I'm currently waiting for parts for a Hall-effect RPM sensor before I run it again.

Edited By Andy_G on 01/07/2022 09:31:25

The NGK CM-6 plug is often used for engines of that sort of size (it is M10 x 1 thread).

I used one for my little (20mm bore) hit and miss engine:

They are readily available and reasonably inexpensive.

In the absence of any information to the contrary, I'd aim for the end of the plug body to be ~flush with the inside of the head, provided that nothing comes too close to the electrodes in that configuration.

Edited By Andy_G on 23/06/2022 10:05:01

"Can it be done a' la cheapskate?"

If you already have a suitalble power supply, sulphuric acid free anodising can be quite cheap and easy.

(My setup: https://misterg.org.uk/anodising-html/ )

If the part mentioned (150 dia x 18) was substantially a solid cylinder, I would use ~0.6 amps for ~2 hrs for a dyed finish.

If you look around the internet, it'll become obvious that people have tried pretty much everything under the sun as a possible dye. Some work, some dont.

Gettin a good black can be tricky. I use commercial anodising dye in a heated bath (55°C). The dye is available in small quantities on eBay for £10 to £15. It produces a good, deep black that has proved colour-fast.

If the dye is leaching out (as per the example above) it would imply that the sealing stage hasn't been successful (the process is Clean -> De-oxidise -> Anodise -> Dye -> Seal ) - sealing by immersing the part in boiling tap water for 20 minutes has worked for me.

Make sure that the process works on a test piece of the same alloy before committing to the part!

(I could do it for you if you covered the postage and could provide a witness sample of the same alloy to check the process first.)

“How are toothed belts sized?”

Generally pitch, width &number of teeth, but it’s a minefield: tooth profile also matters, and there are many. Pitch could be imperial or metric (0.2” is very close to 5mm, for example. )

Can you discern any numbers on the remains of the old belt?

Edited By Andy_G on 14/06/2022 11:27:37

I’ve had the ‘Scheppach’ belt and disc sander for a couple of years and have used it pretty much exclusively for metal (ferrous and non-ferrous).

The dust extraction for the disc sander is assisted by a fan on the motor shaft, but the belt sander extraction is just a duct that doesn’t go near the motor.

I’ve mainly used the belt sander in the vertical position with the horizontal table. I didn’t use the disc sander and ended up adding a crowned roller to drive a narrow sanding belt instead.

I use the blue ‘ceramic’ belts (usually 80 grit) and find that they work well for cleaning up sawn edges and knocking the corners off steel & aluminium parts, as well as sharpening HSS tools & TIG electrodes (I did remove some of the plastic frippery for better access to the belt). I almost always have a vacuum cleaner attached to the dust port which does a good job of capturing the dust and probably helps stop it migrating into the housing.

I think they were £130 when I bought mine. 
 

[Just to add that I managed to break the drive belt the other week, but I would regard that as a consumable- a replacement was readily available for a few £.  ]

Edited By Andy_G on 11/06/2022 09:56:01

Jeepers!

Very impressive work

[Edit: Duplicate post, but it bears saying twice, anyway.]

Edited By Andy_G on 29/05/2022 09:26:25

Jeepers!

Very impressive work.

The original was almost certainly a silicone based 'heat sink' compound, something like this (which does contain zinc oxide).

https://cpc.farnell.com/servisol/200001000-25gm/heat-sink-compound-25g-tube/dp/SAHEATSINKCOMP

(Personally, I'd replace it with similar.)

It would be worth repeating the measurements with the leadscrew removed to rule out the possibility that it is lifting the table as the nut approaches the bearing.

We used to use them a lot at work (some LED, but mostly LCD) - They were branded Cadar though.

I don't remember there being anything special about the on/off switch. It's a while ago, but I'm pretty sure that they charged whether off or on, and could work off the charger if the battery was flat. They often used to be plugged in to the charger 24/7 which tended to kill the batteries after a few years (you only found out if you tried to take one away to use elsewhere - which it sounds like what has happened to yours).

I replaced the batteries in a number of them - they are just a stack of NiCad coin cells inside the end cover; easy enough to change. (4.8V from memory, but don't trust that).

I *think* that the LCD ones may have had a serial interface and clicking on the thumb button sent the reading to whatever was plugged into the other end.

They were very rugged and dependable for such accurate instruments - and they held their accuracy extremely well, even in a shiftwork production environment.

Edited By Andy_G on 11/04/2022 18:22:42

With my recently refreshed knowledge of the aluminium alloy properties, I offer the following:

Generic data on aluminium bronze seems to suggest that the yield strength is of the order of 250 MPa.

(Source)

6082 T6 yield strength is ~240 MPa in sheet form and up to 270 MPa in bar form (depending on size).

(Source)

2014 T6 sheet has a yield strength of ~380 MPa and bar in the T651 condition >420 MPa

Note that 2014 in the T4 condition is back at ~250MPa

(Source)

Obiously this is generic data for the aluminium bronze, and there may be specific grades with higher strength. However the other down-side of aluminium bronze is its density: circa 7.6 vs ~2.7 for aluminium alloys, so an aluminium bronze conrod would be almost 3 times the weight of an aluminium alloy one which in itself will increase the loading on it (and the rest of the engine!) and probably give rise to balancing / vibration problems.

£0.02p

Edited By Andy_G on 01/04/2022 11:32:01

It might be worth trying Coleman Fuel which is available from camping shops, etc. (I presume also in NI).

Mechanical dial indicators with a resolution on 0.001 mm are fairly widely available and have uses elsewhere - could you use one of them against the face that you're detecting with the probe? (Estimate to the half division?)

An interesting and ingenious project - as an aside, how do you ensure the concentricity of the probe to the holder?

Thanks Jason.