Sunday, 23 March 2008

Cut off disk mandrel finished

My first mini project on the lathe is complete. The external 2mm thread took three attempts, the first screw cutting did not work at all. The second was good but too long and when I tried to shorten the screw thread, I snapped it. The only significant difference was that I turned the die so that the flat labelled face was away from the work, I had assumed that dies were symetrical as I've never seen any advice either way. The third screw thread was the right length and the thread was good. I had to drill a little deeper into the body of the mandrel and tap that to take all 5mm of the screw. To allow the cutoff disk to fit, I also needed to thin down the short section of rod nearest the screwhead where it was not possible to cut thread. The slot in the head was carefull cut using a hacksaw.

Unfortunately whilst testing, I managed to break the one remaining cutoff disk. I may make some small card washers to ease the pressure on the disk whilst still gripping it as this is what is done for bigger grinding disks. If I was to make another, I'd made the screw probably 8 to 10mm long. This would mean that when used with the thicker grinding disks there was more thread to grip. This would make the thread cutting more difficult and the screw would be weaker so it's perhaps something to experiment with. It might also be nice to have a knurl on the outer rim of the screw and mandrel body so that it is easier to do up with hand.

Thursday, 20 March 2008

Furnace kit

Given the price of Aluminium in large pieces and the problems with shipping I decided to build a cheap "flowerpot" / "coffeecan" furnace from scrap and cheap materials to do some simple casting which could then be machined.

Everyone on the forums recommended getting a ready made crucible and also some lifting tongs made to fit those. The Silicon Carbide crucibles can take being heated or cooled faster (thermal shock) than the Clay/Graphite ones and hence it is suggested that these are better for beginners. Looking at the shape and capacity an A3 crucible looked the best for my requirements.

I made some investigations and found two suppliers in the UK who could provide both components. (there's more in the US but shipping is expensive).

Supplier 1

A3 crucible: £22.72
F6 lift out tongs: £137.66
Carriage: £8.50
Total: £168.88+Vat

Supplier 2

A3 crucible: £25.00
F2 crucible carrier: £87.64
Carriage: £20.00
Total: £132.64+Vat

Supplier 3

A3 crucible: £16.85
Crucible tongs upto 25KG: £78.65
Carriage: ??
Total: £95.5 + P&P + Vat

I also have a third supplier who came in about the same prices. The price of crucibles I ok with. The tongs are however rather expensive. I appreciate that the crucible lifting tongs are made on demand and that it does require a skilled blacksmith to make them and they are specially design to avoid damage to the crucible. However given that I may be only using them 3 or 4 times a year I could get through a lot of crucible before these tongs are economic. I won't be buying at these prices unless I get to the point where I'm doing casting every week. So I've decided to buy some tongs / fire irons from eBay and see if I can adapt them to my requirements. I've also just discovered that A3/0 is a tiny little cruicible and not to be mistaken for A3 which has a capacity of approx 470ml.

My other problem is finding some refractory clay and/or mortar in a bag smaller than 25Kg, but Wickes looks like a possible with it's 2Kg bags and 5Kg tubs of mortar with the quick drying amusingly taking longer to dry than the general purpose...

I've also just found Hindleys who sell crucibles but I need to check what materials these are made from.

Monday, 17 March 2008

M2 Taps and Dies

As mentioned in a previous blog about the arrival of the mini-lathe, my first project is a cutoff disk mandrel for a dremel like drill.

For this I needed an M2 tap and die set which arrived in the post on Saturday from SFC-Tooling. The body of the mandrel caused no problems and was machined and tapped. The screw on the other hand caused a problem for my first tapping attempt.

I have discovered a technique from Fadmucker for making such small threads. He's made a special die holder with a pre-drilled M2 clearance hole. This means that the die is held perpendicular to the item being threaded.

I've also discovered the following advice on screw cutting from the National Maritime Research Centre who make the point that a thread should have a shoulder if you want to be perpendicular to the load bearing surface. You can see from my diagram above that I do not have such a shoulder, however I don't believe this will be an issue given the size of the screw and mandrel.

My plan of attack is 2 fold, the first is to get hold of some short M2 screws and nuts to check my threads against and the second is to have another go at making the large headed screw for this mandrel.
I've also nearly finished my drill bench which is good because I believe the new pillar drill (drill press) is arriving tomorrow.

Wednesday, 12 March 2008


Not to be mistaken for thermite which is not a suitable building material!!

I was curious to know about these blocks as they are a easy to get hold of in the UK, they are made from recycled material, are a lot lighter than refractory bricks and can be carved using a knife or hand saw.

What is thermalite?

"Up to 80% of the raw material used in the manufacture of Thermalite is pulverised fuel ash (PFA), a stable `by-product' of coal-burning power stations. This recycled material is mixed with sand, cement, lime, aluminium powder, together with processed waste and water, to produce a range of blocks noted for their high thermal insulation."

i.e. These blocks are not just aerated gypsum.

The experts view

What the expert said when I asked him about using these for furnace applications:

"Thermalite blocks in domestic situations are usually serviceable after a fire of approx 900-1000 Celsius, however, exposure is only usually for about 30 minutes and the blocks will have a protection layer of plaster or plasterboard. The protection of your insulating layer is all important, however, asthe blocks dryout they will shrink and crack if they are held togetherby conventional mortar, it would be better to oven dry the blocks priorto incorporation into a structure (to limit their shrinkage potential)and to investigate if a special mortar is required to glue themtogether. We cannot give a definative answer as to wether the blocks will crack due to thermal shock as we have no experience of this type of block used in this application."

Charles from Home Foundry and Casting group suggested that I do a "Myth Busters" on this material.


Blow torch test

A fine flamed butane gas blow torch was held on the block.

The result was that the block glowed red in the area of the flame whilst the flame was applied, the surface of the block was cool a distance of approx 30mm away. When the flame was removed the block rapidly cooled and could be touched with a damp finger seconds after the removal. The estimated temperature for these kind of torches is upto 2400°F / 1300°C.

Blow torch scratch test

In order to determine if the block was softer when hot, a metal rod was used to scratch it. The block is quite soft when cold and the rod produced a medium sized scratch with very little effort. When heated, the block was slightly softer but this was only on the surface for about 2-3mm.

Mechanical Properties

These blocks are quite soft and very brittle, even small bumps and scrapes will cause pieces to be broken off. The blocks can be cut with a hand saw and shaped with tools such as a surform. Don't try to snap a partially cut block as it will break along a completely different line. The blocks are very light and the example shown below can be easily lifted with one hand.

An model makers hearth for small brazing and heat treatment jobs, made from a thermalite block and patched back together with fire cement.

My Conclusion:

I see no reason why this material can't be used for a hearth as above, with no additional treatment, time will tell if it is too soft or if it generates too much dust. It should also be ok as a surround for an aluminium melting furnace. Given that it's a bit soft it needs to be protected with a layer of a harder refractory material on the inside and something such as brick or metal on the outside. For higher temperatures needed for steel and bronze further experimentation is advised to see if it meets your needs.

These results are not endorsed by Hanson the make of these blocks.

Monday, 10 March 2008

Veteran Shed Builder

Not to be out done by Rex my friend Alan has put up another shed, this one is bigger and better than his first and hopefully he did not make the same mistakes as Rex did...

Q: Is this your first shed?
A: Certainly not!
Q: What's different about this shed to your first shed?
A: It's four times the size, the shed is a heavy duty pent (ed. single slope roof, no apex), heavy duty in this case means that the frame is made of 2" timber.
Q: How big is this shed? 18"x6" the other shed is 6"x"8. The shed in mounted on 11 (75mm square) bearers running front to back. The bearers rest on 400m square paving slabs.
Q: From the picture, it look like it's two sheds bolted together, how does it stay rigid? It is not two sheds bolted together. The front and rear panels are made from two preassembled sections to enable easier transportation to site. The panels are held together with M10 bolts available from places like
Q: How long did it take?
A: It took approximately 6 hours to assemble.
Q: How many people worked on this?
A: Four adults bodgers and two little bodgers
Q: What will you do differently next time?
A: Get a bigger shed!
Q: No mistakes?
A: A few but nothing major, some unused holes but a lick of wood paint and no one will notice.

Get your own shed like this one

Sunday, 9 March 2008

Lathe Arrival and Testing

Saupe MD200 Miniturn Lathe

The new/old lathe arrived yesterday and I did a test run of it today to find it's quirks and nuances. I faced off and turned down a piece of scrap metal recovered from an old rotary washing line and got some fairly good results. I intentionally pushed it a little further than it could manage and as expected got some problems but I corrected these in a later pass.

Although I joked that my first project would be to make a washer, I now plan to make a mandrel for my mini-drill's cut off disks to replace the one I made from a bolt that requires me to make the centre hole of the cut off disks larger. I have the material and drills for this but was missing an M2 tap and die, my tap set only goes down to M3. Thanks to SFC-Tooling on ebay, I've tracked down some taps and a die for a reasonable price, my usual suppliers Axminster and Chronos were charging significantly more for these items.

Facing off a bar

Friday, 7 March 2008

Book Review - Tool and Cutter Sharpening

The Tool and Cutter Sharpening book, pretty much covers how to sharpen everything that you might have in your workshop, the only exception I've found so far is that the chapter on drills does not mention masonry bits. The book is in the popular Workshop Practice series and is written by Harold Hall

The intro starts with details of different types of grinder; Vertex, Quorn, Worden, Stent and the "off hand grinder" which we would commonly know as a "bench grinder". It mentioned types of grinding wheels and the importance and use of a rest.

The middle chapters walk you through each type of item, drills, lathe tools, milling cutters, screw drivers, centre punches and woodworking tools. The instructions are detailed without being patronising.

The final chapters have some how to make projects for a grinding rest, jigs for grinding end mills, square and round workpieces, very small drills and four facet grinding of drills and details of how to modify your bench grinder to take a cup or saucer grinding wheel.

I'd recommend this to anyone who's got a few things to sharpen and either has or is thinking of purchasing a grinder.

Tuesday, 4 March 2008

Stirling Engine Used to Cool PC

Most model engineers will have heard about Stirling Engines, some may have even built a few. However one of the engineers at MSI had good idea of putting a Stirling Engine inside their computer to cool the processor.

There's no video at the moment but here's an example with a slightly larger setup.

Monday, 3 March 2008

Shed Builder

I was lucky enough to buy a house with a shed already in place at the bottom of the garden. Other's have to build their own from scratch or from a kit. My friend Rex and family assembled a "Rowlinson" Overlap Shed, 2.07 x 1.17 x 1.82m this weekend for his sister.

Q: Is this your first shed?
A: Yes.

Q: How long did it take?
A: About 5 hours

Q: How many people worked on this?
A: 3 adults, 6 children

Q: What did you use for the base?
A: 10 paving slabs arranged in a box shape

Q: What would you do differently next time?
A: I broke a paving slab by jumping on it, trying to level it, my dad attempted to use his chainsaw to trim the weatherboarding, it just ripped it up.

Despite this, the end results seem to have turned out alright and the shed has been christened "Beatrice".

Saturday, 1 March 2008

Bench work in progress pictures

The bench framework and top assembled, need to attach the edging and sanddown and paint my screw fixing holes. Apart from one joint where the 2 screws clashed in the middle the construction went fine. The shelving that forms the back legs has also been repaired with some angle strip from the local B&Q.

Workshop Practice Series