Mass production, tooling, strategies and budgeting.

This blog could be titled, How to get it wrong.

I'll start with the story, then I'll point out the failings.

A few weeks ago I made a new heater for my solidoodle 3d printer, I was quite happy with the results, despite having broken a drill bit in my heater block, I got around that, and I decided that was my fault, I clearly wasn't drilling the hole straight, it was a small drill bit, and they often break anyway...

When I bought the aluminium bar to make the hot end I had decided that I would probably want to make something else anyway, so I got a 2 meter length.

After making that first hot end I decided that I was going to make and sell a whole load.
I had enough aluminium bar, I had bought a hundred heaters at the start of the project, (knowing that I could sell the heater elements on their own!)

So I started cutting up that long bar of aluminium into 100 small pieces.
by about the 3rd piece I gave up and went to ebay and bought a small hobby band saw. -this worked great for cutting the aluminium, right up until the blade broke -though this had come with the saw, (which only cost £30), and had made 99 cuts, -failing on the last)

After this I got my set square and scribe and marked out where I needed to drill holes on all 100 blocks that I had cut. then I centre punched them. -this is time consuming, that was 600 holes that I marked!

After this was done I decided that I'd start drilling, rather than drilling by hand I decided that I'd use my fathers pillar drill, a Draper tool, I dutifully loaded the drill bit into the chuck, and set about drilling holes, I started by drilling 2.5mm hole through all of the holes I'd marked, a lot of the holes needed to be 2.5mm, others would benefit from a pilot hole being drilled anyway.

However I found that on the point where the hole for holing the thermistor met the hole for the screw securing the thermistor, the drill bit would catch and break. this was the same problem I'd had with the hand drill, but now I was getting this with a machine drill, one that was square, level and had no lateral forces, clearly there was a problem with the way that the cut was being made, swarf from the hole was catching and causing the bits to break at an alarming rate.

Eventually I managed to get a few holes drilled carefully that did meet, (afterwards I bought some 2.5mm end mills that I would use in the drill to make these holes meet more successfully!

At the end of the time I had set aside that day I had 11 pieces half made, I had the holes for the thermistor set-up drilled successfully, and the long hole through the block pilot drilled. at this point I'd been at it around two hours, and decided that was enough... -and besides the drill had gotten quite warm and I thought it could use a rest!

One morning the following week I decided that I'd continue my project. however within ten minutes of starting the drill the motor had caught fire.

In the end I took the pieces home and finished the first batch with a hand drill.

I tapped them and installed the heater elements.

As it's a new month I've been paid and gotten some more money to spend on this project I've now ordered the thermistors, wire and heat shrink to finish these heaters up.


So... let's look at where I went wrong.
First, I'm hoping to sell these for around £12 - £14, this is in line with what others have sold for on Ebay.

the heaters were £130 + £15 import VAT for 100
Aluminium bar was £10
Thermistors are£70 for 100
heat shrink is £5 for the 6m of 1mm heat shrink I need
and £3 for the 5m of 3mm heat shrink I need.
wire is around £2 for 10 meters, (and I need 200meters) so £40
the grub screws cost around £15

So a quick sum up looks like I'm nearly £250 in the hole with materials.

Postage on each item is expected to be around £1. (so that's another £100)
Ebay will take ~£2 per item, (£200)
and pay pal will also want their 10% (£1.40 per item, times 100 = £140)

so that'll be around £700 of costs.
I'm hoping to sell these for a total of £1400

but here's where the problem starts....

now take roughly 25% of that away in taxation and national insurance that I'll need to declare. that's £175, leaving £525

Trying to do this cheaply has meant that I broke around £5 of drill bits whilst trying to make the blocks, and that £10 saw blade for the band saw.
(leaving £510)
I'd busted my dads pillar drill, because it's a hobby tool, not an industrial tool, it's meant to spend about 30 seconds being on, then have ten minutes to cool down, now spend nearly three hours in constant use, so that it over heats, and breaks down the insulation, (and then catches fire)
a complete replacement is around £300, second hand maybe £150, or a new motor will be around £100
My "profit" is now a pretty shabby £400...
then I spend a couple of hours cutting up the aluminium bar, a few more hours in front of the drill, a couple of hours sourcing materials, I'll conservatively spend probably 15 minutes per item with listing on ebay, talking to buyers, packaging and going to the post office to actually post the things.
(that's 1500 minutes, or about 30 more hours). I spend around an hour designing the thing in the first place.

Based on the initial ten I have that's 6 hours of machining and making,
So that 100 will be about 60 hours of machining, plus 30 hours of listing and posting.

So that £400 I've got remaining will need to pay for about 100 hours work. about 2/3rds minimum wage.

in other words.
I started out thinking, cool, the parts for this will make me loads of money, I'll spend about £2.50 on an item that I can sell for £14.

But,
using hobby tools has increased costs due to breakages.
Using hobby tools has meant that I can't work for more than an hour at a time without significant machine downtime to cool off, increasing the amount of time take to produce parts.
Funding this venture myself has meant that I've had to wait until pay day to get more funding. - I could have taken this to a kikstart project, but them I'd have 100 angry customers breathing down my neck saying that my lack of planning or prep wasn't their fault, and where is their money etc.


The long and the short of it is:
before you decide that you want to give up your day job and live the dream of running a tech startup. do your sums first. be realistic.
I was wishfully thinking that I might get around £700 for what would be an easy day stood at a band saw and a drill. -actually I was thinking I could use an ordinary hack saw to do this work!

What I though would be around £100 per hour I'll retired a millionaire next week, has actually resulted in being a drain on time and resources. Maybe with a few thousand pounds of investment for industrial tooling I'd do better -but I doubt that also!

Electronics lessons: Mains Power -single phase and three phase

Whilst writing this blog I've stayed away from things that I would consider dangerous.

That is to say I've completed some projects that I've felt were either too big to document, (like when I put up my new storage shed in the garden and put electrics and lights etc in.) -at the time my thoughts were like this. it's OK to tell someone to stick bits of wood together to make a speaker, it's OK to say to people use this step down transformer and deal with the safe voltage that comes out the other side. I even thought it fine to tell people to stick electrodes into water to generate hydrogen/oxygen gases!

But big scary voltages have been something that I've stayed away from, the thing about mains utilities is that, you can smell gas, and know to shut off the supply and get out. you can see water and hopefully have the intelligence to get out before drowning. Electricity is completely invisible, it's not a substance, it's a force.

Anyway, that might give you an insight as to how I feel about mains electricity. it's dangerous to the point of deadly, and too much confidence can lead to mistakes that ultimately can kill you.

As a point of reference I live in the UK, this means that for me, voltages come in 120v for site tools, (where the 120v is considered safer due to lower voltages) this voltage is obtained by using those little yellow transformer boxes.

240v comes into every homes, (at least every connected home, I suppose off grid homes might make their own standards).

440V is considered industrial and is what most three phase power outlets are going to be using.

Voltages are measures with respect to neutral, live - neutral.

Single phase

Single phase power is an alternating waveform going from the positive extreme of the voltage swing to the negative extreme of the voltage swing in one wave form.

Single phase is what I've mostly dealt with, it's easy to visualise, easy to look at and easy to understand. remember that the positive is measured with respect to neutral, not with respect to ground.

Sometimes a single phase supply is actually a 2 phase supply, where instead of a virtual earth, or earthed neutral, there are two hot phases where the phases are 180 degrees apart.
the sum of the phases is zero, (e.g at 0 degrees phase 1 is 0v, phase two is at 180 degrees and is also 0v, at 90degrees, phase 1 is +120v and phase two is 270 degrees and -120, (+120 + -120 = 0v), the total potential difference between the two phases is 240 volts, (120 - -120 = 240)

Three phase

Here's where it starts to get a little more complicated.
Now there are three phases, each phase is 120 degrees behind the next, they are still sine waves, and they are still measured with respect to neutral, but there is no neutral in the transmission line, -when power enters your premises in a single phase set-up there is a live and neutral line. when you get three phase there is only 3 live wires, no neutral. (you can make a neutral by connecting all the phases together, because the sum of the phases is zero) -but I'll cover that in a later lesson.

You can see at 90 degrees now phase 1 (blue) is at at the top of it's rising cycle 240v, and phase 2 (green) is just coming up from the bottom (so during it's rising cycle) and is -120v, whilst phase 3 (red) is getting towards the bottom of it's falling part of the cycle, and is -120V
240 + -120 + -120 = 0

Colour Codes

Colour codes for wires are important, in that they will let you know what wire does what. everyone knows that green/yellow stripe is earth, and it's safe to touch. but what if I wired a plug so that the earth wire was used as a live conductor.
it's just a bit of copper, fundamentally there is nothing to stop me from doing that, provided I wire the other end the same way, where's the problem?

The problem is what happens when I'm out, and whatever appliance I've wired badly breaks, what if my wife/girlfriend/boyfriend/husband/friend/son/daughter/mother/father/grandparent etc decides that they just want to check the fuse on the plug, then they see the wires connected wrongly, so think that might be the problem. or something see's an earth wire, and decides that they can splice that wire to earth something else, -except it's not earth, it's live, and they are probably now dead.

Colour codes are set by the IEE.

for single phase systems.
Brown = Live, (the old colour was red)
Blue = Neutral, (the old colour was black)
Green and yellow stripe = Earth, (the old colour might be plain green)

for three phase systems,
Brown = Phase 1 (old colour was red)
Black = Phase 2 (old colour was yellow)
Grey = Phase 3 (old colour was Blue)
Blue = Neutral (old colour was black)

This means that if you are adding new wiring to an old system, don't just connect the new blue wire (N) to the old blue wire (P3), or the new black wire, (P2) to the old black wire (N)

you may also find three phase systems where the conductor colours are Brown, brown brown for P1, P2 and P3, with a blue for earth.

Earth (as always) is green yellow stripe.

earth may also be the bare wire in fixed installations, (where solid core wire is used rather than stranded wire).

Filing, -photographing documents en-mass

Filing is something that I'm both good at, and bad at.

There comes a point in most peoples lives when they are quite literally bogged down with paper. from bank statements, credit card statements, phone bills, TV bills, water and gas bills, old insurance documents...

All pretty important stuff important at the time to keep in case of dispute, and important later on as an aid to memory, (like remembering how much something cost when you bought it!)
having a receipt past the warranty period seems silly. But given a few years ago my house was robbed and I lost several possessions, it now seems worthwhile keeping receipts for things, just in case the worst should happen and I end up in the position again of trying to remember, exactly what model of tool did I have...

Because -let's face it. with an expensive tool like a welder you don't want to say I had a 260Amp MIG welder (when in fact I had a 150 Amp welder), if the original items were ever recovered you'd have some explaining to do as to how you claimed for something that you just didn't have! on the other hand, you don't want to err on the side of caution and say I think it was the 90Amp model, because then you won't have the same tools that you started off with.

So, it seems logical to scan or photograph documents.

To that end on Sunday I had a filing day. a day where I take the large bag of bills, bank statements and receipts that I've let pile up over the past few months or year and commit them to a digital format. Rather than scan them as I have done in the past this time I decided that I'd photograph them as this would be faster.

So I rigged up a little ledge to put my phone on such that it was at a distance that a single letter would fill the photo taken.

This involved a length of wood which I balanced on top of a few items with my iPhone sat on top of it. to take a photo I could just press the screen, and then move documents into view, press, put another document in view (on top of the previous letter so I didn't even need to fiddle with the document to align the letter in the phone screen), then press the take photo button.

It ended up as a pretty slick process, I got a whole ream of documents, (yeah actually 500!) scanned in a few hours.

The only think left to do is sort them into folders:
(for example my bank statements are sorted into a folder called bank, and they are named by the date the statement was sent. yyyy-mm-dd that way when sorted into folders they appear in chronological order and can be viewed sequentially.)

Here's a picture of the make shift camera holding set-up that I used to speed up the photo taking process.

Making a new hotend heater

Annoyingly my replacement hot end for my solidoodle has failed again. it did last a lot longer than the original hot end that came with the machine, but it was fairly obvious that it would fail again.

The mode of failure is that the nichrome wire is getting too hot and melting through the Kapton tape, this is turn is making short circuits, and reducing the heater resistance, this is making more current flow, and the power to the heater is increased, I'm seeing a lot of max temp reached where the hotend starts to peak well in excess of the max temp permissible, (the max temp is to protect the peek)

But also the sudden rushes of current cause cause the power supply to stall, I've had steps being skipped, sometimes I've had axis appear to just re-home themselves, so instead of a single layer skipping, the entire model will just move two inches to the left have way through a print.

So this time I'm going to go all out and create a new hot end.

I'm going to base my design on the Jhead style heaters, with a block close to the nozzle, but instead of using a resistor I've decided to use a small ceramic heater.

Instead of tying my heater and barrel to the nozzle (which I may want to change to have greater or smaller nozzle widths) I'm going to stick with the M6 barrel of the solidoode, I'll stick with the removable nozzle, and I'll make a heater that can be screwed on and off just like the heatcore design could.

To start with I've located a 40w ceramic heater online that comes in a 23mm long 6mm diameter tubular package.

This will be my heater.

My block that will be used to store heat will be aluminium, (it's easy to acquire, relatively cheap -at least cheaper than brass)

The block will need to be at least 20mm wide to accommodate the 23mm heater, (it will not matter if 1mm sticks out either side -and this will help keep the wires away from the hot metal.
the block will be 10mm thick, this should mean that there is 2mm either side of the heater,
this will also allow for a 3mm hole to be drilled to install a grub screw to hold the heater cartridge in place.

The heater will be 2mm from it's opposite side of the block, and 2mm from the barrel of the machine, the barrel is 6mm wide, here will need to be at least 2mm on the opposite side of the heat block, (therefore the heater block must be 20mm x 10mm x 18mm, the most convenient size is 20mm x 20mm x 10mm)

Lastly the thermistor must also be installed in the printer, and must be thermally bonded reasonably well, to achieve this I plan to use heatsink style thermal compound and a second grub screw to ensure good contact.

Materials needed,
1 Aluminium block, (20mm x 18mm x 10mm) -I cut my block from a length of bar that was 20x10 x 2000mm
1 heater core, I bought mine as a 40w heater, but the measured resistance is actually 4.2Ohms, so it's actually a 34W heater.
3 grub screws I'm using M3 x 3mm
Thermistor -I'm re-using my original.
electrical connector - I'm re-using my original

Tools needed (at a minimum)
hacksaw -I'm using a B&Q value junior hacksaw -that cost 99p!
Drill
5.5mm Drill bit
2.5mm drill bit
6mm drill bit
M3 Tap
M6 Tap
Ruler
scribe for marking

so, here's the process.
First mark 18mm from the end of the bar

then cut off the aluminium block


now you need to use a scribe to mark where you want to drill



(the measurement that is missing here is that the M6 hole is centred 9mm from the far edge)

first drill the long hole through the block, start with a 3mm hole and then enlarge that to a 6mm hole

then drill a 2.5mm hole next to that, about 5mm into the block

now drill a 3mm hole and enlarge that to a 5.5mm hole (ready to be tapped for M6) in the face of the block

test fit the heater to make sure it fits

now using a 2.5mm drill bit drill three holes in the top face of the block.

unfortunately my drill bit broke inside the last hole, so I put a different hole in the side instead -the drill bit is still stuck in the block

now you need to use the M3 tap to create a thread on the two 2.5mm holes that are drilled through to the 6mm hole, and also in the final 2.5mm hole, (this should be on the top, but mine is on the side thanks to the broken drill bit)
Then you need to use an M6 tap to create a thread on the 5.5mm hole that goes through the block.
now we come to assembly.

the heater slides into the 6mm hole.
the thermistor slides into the 2.5mm hole.
the thermistor is secured with an M3 grub screw.

and the heater secured with two more grub screws

Now I've pulled the whole connector off the original green heat core wires, and attached it to the new red heater wires.

You need to remove the extruder from the machine, (the block catches on the carriage if you don't remove it to turn it)

then you can screw the new heater onto the machine and replace the nozzle.
after that the only thing left to do is re-mount the extruder, re-connect the wires and start printing!


The heat-up time is more or less exactly the same, and the stability of the heater is actually probably a bit better than the original heatcore, (looking at the graphs in RH)