Member postings for John P

Google tens machine there are a lot of different circuit diagrams
around for these things.

Look at this and it will give an indication of how these things work.

https://www.learningelectronics.net/circuits/transcutaneous-electrical-nerve_03.html

John

With the setup here to divide 50 divisions the sector arms are set to give
an advance of 16 holes not including the hole the index pin is in.

With this set up as shown the index pin arm is rotated clockwise and
drops into the hole as it passes over the lower sector arm ,the sector
arms rotate anti-clockwise to set the position for the next division.

John

In the absence of 1 to 1 tuition there are plenty of videos on this subject
Google surface grinding and see what comes up ,from there on
is it is just a matter giving it a try and learn as you go ,its not really that hard to do.

Here are some to watch that may be of use.

https://www.youtube.com/watch?v=npybvhWYklc

https://www.youtube.com/watch?v=iMHksf17oqE

https://www.youtube.com/watch?v=OwPCHbAOqw8

https://www.youtube.com/watch?v=7tN_uGHNknM

https://www.youtube.com/watch?v=CXXfez5I_0A

John

Lots of useful information here on the correct blade selection.

https://www.lenoxtools.com/Guides/LENOX_20Guide_20to_20Band_20Sawing.pdf

14 tpi is most probably too fine for a 2 inch copper bar, a 4 or 6 tpi
or variable pitch blade is best .Coat the blade with rocol neat cutting oil
or Trefolex to prevent pick up on the teeth. Slowest cut speed the machine has.

John

Try metal 4u

https://www.metals4u.co.uk/materials/stainless-steel/stainless-steel-round/1254-p

60 mm dia 316 x 120 mm long £ 54.35 + post

John

Posted by Andy_G 03/07/2022 21:26:15

(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.

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First of all you have made an impressive job on this Kamps engine design ,the EGT
is very low ,did you find out the top end speed and have you done any thrust measurements?

I used to be a member of the GTBA but let it lapse when they went on line only
as back then i had no internet connection , i still have one of the original GTBA
commissioned turbine wheels seen here in the photo along with a Wren
MW 54 wheel also there is a 66 mm wheel and stainless cast NGV
also from Wren. Since they disappeared these parts i guess have gone.
Some of these parts are seen here ,on the left Some Wren mw 54 parts
a bought turbine wheel , milled NGV centre from 316 ss , compressor wheel a
free-be from a collection of them, 3 off part machined diffusors.
Towards the centre top some milled 718 turbine wheels and the GTBA and
Wren wheels ,on the right some FD 3/64 parts , in the lower half a nearly
reclaimed disc of inconel most probably 713 from a scrap radial
inflow wheel.

I seem to remember that before the availability of cast turbine wheels
inconel slices about 6 mm wide were around the £35 mark ,that was over
20 years ago , by buying a length of inconel bar brought that price down to about
£8 to £10 ,of course you still have to slice it up by whatever means and the mill
the blades.

That is why that i said it would be a better option to buy a ready made wheel
as the real cost is only the difference from buying the material and the tooling
and the time minus the cost from the ready made item.

With that in mind the home made compressor wheel milled from the solid
seen here and in previous photo's is a similar situation the aluminium blank
probably about £5 or £6 plus all the work to get to finished job when you can buy
a new cast wheel for £14 + vat and free shipping does not make it really
worth while.Although i have to say that you do learn a lot in doing something like this
also as i wanted a reverse rotation wheel it is a simple matter to change
some of the axis polarities to be able to do this ,in the photo here is a wax
test cut reverse rotation wheel alongside the aluminium one.

Seeing the last part that you had written about the GTBA radial inflow project
is not really surprising as a complete rotor set is only about £35 for an engine
similar to the original JPX type engine .

The last photo here shows the much modified Shreckling FD 3/64 engine
installed in an airframe ,you can just see parts of the fuel tank in front of the
engine ,its bigger than the engine,the model has never been flown.
Most of the parts seen here were made 10 to 15 years ago.

John

Posted by Steve355 02/07/2022 09:54:21

Morning

Is there anyone out there who has advice for a total beginner at sand casting?

I made a waste oil burner and furnace, after a lot of tinkering it’s working pretty well and can
get up to 1100 deg C or so without too much trouble.

My first project is to make some brass sanding blocks for making woodwork moulding planes.

I made a pattern on a 3d printer. I used play sand (fine and consistent) and about 10% fireclay
as DIY greensand.

I used a cast iron flask, packed down the pattern in the sand vertically and removed it carefully.
I melted down the brass and poured it in. The result was, well, roughly the right shape, but it had
a big nodule on the bottom (presumably caused by the pouring brass) and a terrible pitted finish.

of course I can sand out some of the pitting, but that’s not the point.

Does anyone with experience have any tips? See pics. Yes it’s terrible, I know.

Steve
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I started casting around 1984 ,i was at a Model engineer show and one of the stands
was selling crucibles along with give away leaflet , i bought one i think it was about tenner.

That was about as much as i knew about casting,back then there was no internet and
there was no one that i knew of that had done any casting,first problem no sand, i had a ring
around after looking through the Yellow pages most of these were industrial type suppliers
and came with the warning of the usual that's too dangerous you'll end up killing yourself
(much the same as you often see on this forum), we only supply 20 tons at a time.

I phoned around some local foundry's and they were most helpful ,bring some buckets
and you can have some ,i still have the same 2 dustbins full of sand now.

My first castings were done using an old tin oil drum full of coke and an old cylinder
vacuum cleaner to provide a draught, some of the early castings were nothing more than
useful blobs of metal but you learn as you go along.

Eventually i got fed up with the tin can and coke furnace and built this modified Dave
Gingery furnace (in about 1989) supposedly will melt 20 lb of cast iron in 45 min i don't know if it will
I've never tried it with iron , an A8 crucible will fit inside.
(First Photo)

The thing is when you have done some of this you tend to forget how much equipment
that you have accumulated over time, the furnace the crucible some sand and then all of the other
stuff that you need lifting and pouring rings , moulding boxes, patterns and some
decent safety equipment and so it goes on ,it all adds up to some expense in both
money and time.

The 2nd photo here shows some of this stuff in the foreground some moulding boxes,
crucible , lifting tongs, pouring rings , behind , a copy of Luckygen's sand muller a recent
addition ,at the back leather aprons leggings face shields and gloves.

I don't do much foundry work the last time was about 15 years ago but in the next week
or so its getting fired up again if the weather stays fine. 3rd photo.

It should be much easier than when i started as there is so much stuff available now and
useful advice , there's Luker, Pat J, and Noel Shelly ,worth looking at the videos
from Luckygen ,Old foundry man and Myfordboy they will all have something that
will be of use to you.
You just have to stick with it ,work carefully follow some of the advice and watch some
of the videos .

John

Some useful download plans can be seen here from Gerald Rutten (zip files)
http://www.gerald-rutten.nl/turbines.htm

They use the same gas container as the early Shreckling engines ,the most thrust obtained from the engine that i made was about 6 lb ,i think the GR 180 in the plans above produces about 36 lb.

---------------------

https://www.turbomaster.info/eng/applications/compressor.php

shows the sizes of nearly all made compressor wheels and is a
useful reference.

-----------------------------------
The 2 compressor wheels here (1st photo) were from Aliexpress ,the one on the left
is a K27 wheel 47.3 dia inlet and 73.9 dia od 14 blade
the one on the right is a TO4B 45.8 inlet and 70 mm dia od 16 blade.

------------------------------------
The 2 compressor wheels shown here (2nd photo) , on the left milled from
2014 t6 aluminium 68 mm od for KJ 66 engine , the one on the right
is a KKK 5326 123 2038 cast wheel also for a KJ 66 engine.

---------------------------------------
The turbine wheel seen here (3rd photo) is for Shreckling FD 3 /64 turbine engine
milled from 718 inconel 20 years ago, perched on top of the remaining 17 inch
of 2 3/4 inch dia inconel 718 bar .

It is perhaps not worth making a turbine wheel from solid these days
unless you already have the material and the means to mill them ,back then
ready made wheels were only just appearing from the GTBA when they had a
batch made for members of the organisation.

www.jetmax.ch sell ready made wheels from about 66 to 82 mm dia from
about 165 Euros which suit the KJ 66 engines and also the Gerald Rutten
turbines.

John

Posted by Brian John 30/06/2022 13:07:03

Watching this makes me want to build one just for the sound alone !

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Some useful download plans can be seen here from Gerald Rutten (zip files)
http://www.gerald-rutten.nl/turbines.htm

Photo here of some Wren MW 54 parts and some KJ 66 parts.
On the left wren MW 54 ,in the centre KJ 66 milled from the solid
compressor wheel and blank behind .

New compressor wheels can be found on Aliexpress for less than £20
like these here in the 2nd photo.

Standard 608 bearings can be used and are good to about 120,000 rpm
but have a short life . A cheap alternative is to re-ball a standard bearing
with Si3N4 ceramic balls ,the inner race needs to be reground to be able to
fit with a phenolic cage or fill the whole bearing to make a full compliment
bearing.

John

Just as an update on threading indicators see this on lathes uk

http://www.lathes.co.uk/universal-thread-dial-indicator/index.html

John

Aliexpress sell full ceramic bearings for somewhere around £4 each depending on size some will work up to

800 C only at low rpm (200) there are hundreds of them , type in " ball bearings high temperature" to scan through,not able to put reference on here as it will be taken down.

John

Michael

This looks about the same size as the one in the springer link .
Good luck!

John

This may be of some interest for making a high speed machine spindle.

https://link.springer.com/article/10.1007/s40684-019-00105-5#Fig7

John

Posted by ega 20/05/2022 10:59:48

John P:

Is that a Quorn spindle in your photo?

----------------------------------

No, it is 1 of 3 spindles made for this machine as internal
grinding spindles ,this one has a Quorn nose and can use all of the
Quorn wheels that i have.
Similar construction to the Quorn spindle but slightly larger ,uses
17x35x10 mm bearings .

John

Posted by William Chitham 19/05/2022 18:55:52

Never used one but a pencil type air powered die grinder might be an option,
maybe they don't use so much air as the standard sized ones. Very fast and
not too expensive if you already have a compressor. I noticed this one in MSC's
last advantage sale:

Jupiter Micro Die Grinder

William.

--------------------------------------------------
This is the same pencil grinder from J&L ,runs through an air
pressure regulator at 90 psi from a 2 HP 25 litre tank compressor.
Compressor will cut back in after about 2 to 3 minutes to keep it running .
Same sort of pencil grinders from Aliexpress from about £12
and free delivery.

John

Posted by Mark Rand 15/05/2022 09:39:49

I'll leave people to their apprehensions and assume that none of them have
ever had to do any form grinding, face grinding or endmill sharpening.

-----------------------------------------------------------------------------------

How very true ,bring up any of these grinding type of threads and you see
the same old stuff about the dangers .
I sharpen my milling cutters using a cnc machine ,add in the mix of grinding
wheels and computers to run them and a whole new bunch of scared to get out
of bed types will be posting on here.
Despite the abundance of so called experts on grinding there seems to be
very little or none written on the practicalities of actually doing it.

John

Posted by Andrew Johnston 13/05/2022 14:07:26

Best to sit down and put on the seat belt before looking at prices for CBN inserts.

Andrew

Cheapest price on Ali******s iv'e seen is £4.59 for a VNMG160408 and free shipping.

John

Buying a reputable make or from professional suppliers is no guarantee of getting a good
wheel these days.
The wheel seen here on the left is a Norton wheel from RS not cheap ,the mounting area
was like a rollercoaster track ,the balance was poor but easily corrected when mounted
on this heavy hub ,the centre of gravity is moved to the back of the wheel where there are
two balance rings to even things up .
The other three wheels here all from China all cheap and very well made without the
problems the Norton wheel has , the 2 Quorn wheels are perfectly balanced as is.

John

In this video Dan Gelbart shows at about 5 minutes 45 some reworking
of grinding wheels.

https://www.youtube.com/watch?v=sFrVdoOhu1Q

For those of us who don't have such facilities China is your friend
via aliexpress who sell diamond core drills which can easily
modify or make up stones from old or even new grinding wheels
such as these.
John

Posted by Rich2502 09/05/2022 14:15:41

Any one retro fitted a leadscrew to a small lathe? ( 15-20" between centres )

There are now motor controlled set ups withh off the shelf ballscrews that require
no gear train so that would cut out a lot of the work.

Is this a practical project or a rabbit hole ?

------------------------------------------------------------

Warco cnc conversion Mew 207 through to 212,
a bit bigger than your machine but the principle much the same.
John