Motors

After much discussion on the RepRap forum, I have ordered 3 of the following stepper motors:
NEMA 17 type, part number FL42STH47-1204 from Motion Control Products Ltd, webpage http://www.motioncontrolproducts.co.uk/product_info.php?cPath=4&products_id=47.
Basic details are Voltage: 4V, Current (phase): 1.2A, Inductance (Phase): 6mH, Holding Torque: 45Ncm, and it is a 1.8 degree stepper. Heavy, though at 150 g, but cheap at £9.26 each.
From trials of other motors it seems that the holding torque never gets to the rated values (of ~ 0.3 Nm and upwards) on the motors tried by others because of the current (ie electric current A) limits imposed by the controller electronics.
That's if I understand it....

Motion Control Products sub-total = £45.75 inc P&P

• Stepper motor, part number FL42STH47-1204, £9.26, x 3

Running total = £142.77

I've cut the 3.6 cm edge off the MDF now. I've just tried screwing through the MDF - I need to make the pilot holes 3.5 mm next time, and also make the countersinking err towards larger rather than smaller for a flush finish.

When marking through holes to locate drilling holes in the y and z angles, make sure you mark the outside, not the inside, or the measurements won't be right! Nearly got that all wrong.

I've been looking at http://www.reprap.org/bin/view/Main/McWire_Cartesian_Bot_1_2 to work out where to attach the y-rails to the x-stage, and two pictures show them in very different places. I have plumped for centring the rail across the stage to see if that works.

Here is a diagram of the y-rails:


I have also chosen where to put the fixed side bearings, or PTFE disks in my case, and will experiment with springs and the swinging brackets. I'll put up the x-stage diagram when it's decided.

Drilling

I spent yesterday evening and this morning hunting for suitable stepper motors. Unfortunately, the requirements don't seem to have been quoted anywhere. Actually, the fact that you need 3 stepper motors at all has been omitted from the parts list for the McWire on http://parts.reprap.org/part/module/McWire+Cartesian+Bot+v1.2 and for the Seedling on http://parts.reprap.org/part/module/RepStrap+v1.0+%22Seedling%22!

This afternoon I marked all the base drill-hole positions with a centre-punch and hammer and using an electric drill drilled the 3 mm pilot hole in the MDF, then used the countersink bit afterwards. I used a 1.5 mm drill bit, then the 3 mm drill bit and finally the 5.5 mm drill bit to go through the metal pieces for the base. This helped keep my drill-holes centred on my mark and therefore as accurate as I could make them. I filed off the burrs with my hand metal-file.
Before assembly begins, I shall use these pieces (drawing through the holes) to mark the positions of the holes on the rails and angles for the y- and z-stages, because they are to be assembled in the same way.

Marking for drilling - or more sawing....

Well, I said I wanted to post about errors as well as successes, so here's the first. Having made my MDF base 24 " wide, I realise now that sitting the metalwork on the MDF won't give the x-stage stepper motor any room at all, so I am cutting 3.6 cm off down the left side of the MDF base when looking at its bottom face, which is where I am marking the drill-holes. I may need to move the whole assembly backwards, but time will tell, or I may need to use feet to lift it off the floor, but as I don't know what motors I'll be using yet....

Anyway, I have drawn diagrams of where to site the drill holes:



I shall use the countersink 5 mm screws I bought earlier today. I have measured the top of the screw at 9 mm, so I have also marked a 9 mm line across the marked positions on the MDF so that I can drill a countersinking hole to the right size - drilling from underneath. I shall also drill 3 mm pilot holes right through the MDF and 5.5 mm holes through the metalwork.

The nuts and bolts of it all

Screwfix and Wickes are decidedly short on choices of bolts. So much for saying I'd go get the screws etc as and when I needed them since Screwfix was only up the road.... I picked what I wanted off the website but when I got to the shop it wasn't in their catalogue so they don't stock it.
So instead of buying a small number (25) of the right size bolts I ended up buying a whole multi-pack of assorted sizes for rather more expense, because that was the only option. And why do bolts come in packs of 10 or 25 whereas the nuts only come in packs of 100?

So I ended up buying the following:
Screwfix sub-total = £24.30

• countersinking drill bit, part 11311, £5.37
• machine screw pack - for 12 countersunk 5 mm diameter bolts at 2 cm length for fixing rails/angles to MDF - part 13352, £14.99 (ouch)
• 5 mm nuts, pack of 100, £3.94

Running total = £97.02

Unfortunately, I forgot to get the 8 mm nuts to fit the threaded rods......

BIG CUTS across the board...

I used my new workbench and jig-saw to cut the MDF - took about an hour. Then I did the threaded rods, cutting through the hardened outer with the saw and then snapping off. The first one was harder, the second cut easier and the third cut middling! Guess the material isn't consistent. That took another hour. Then I cut the U-shaped channels. Although I started with the jig-saw, it was easier, actually, to use my Boa saw (a kind of hacksaw, only better for this kind of thing).

The workbench has well and truly been christened - I used it at three different heights depending on the job in hand, but I took a graze off the top of one handle, off one side of the top and onto the metal top support too! (Design-flaw: these supports need to be lower to avoid the jig-saw blade depth.)

I filed off all the sharp metal ends as I went with a little hand metal file.

Cutting the aluminium angle and filing off any sharp bits took about an hour and a half (again starting with the jig-saw but swapping to the Boa) and cutting the PTFE took under an hour. Don't try cutting this with a jig-saw - just doesn't! I filed all the fluffy cut edges off with the same metal file.

The only thing I've not cut is the PTFE rod. I haven't decided exactly what I'm doing with that yet.

Markings continued (still)

Today I marked up the aluminium angle,

two pieces at each of the following measurements:

• 9 "
• 6 and 3/8 "
• 9 and 1/16 "
• 5 and 15/16 "

and one at 2.5 ".

Hmmm - interesting

Marking onto PTFE turned out to be interesting - pencil didn't work at all, and trying to make small measurements marks with a ball-point pen was a bit hit and miss, but marking lines with the pen was largely fine.

I don't know how long to make these PTFE strips (they're 0.5 " wide), but the instructions (http://www.reprap.org/bin/view/Main/McWire_Cartesian_Bot_1_2) say there are 12 of them, and the total number listed in the BOM is 24...

In the pictures they look about 2.5 " long, judging against the size of the stages.
Meanwhile, the BOM under (http://parts.reprap.org/uniqueparts) states 24 " of PTFE strip - although that may just be the size of the supplier's part.

So, I'm going to go with 2 " per piece of PTFE.

Workbench

Finally got the workbench finished. Ish. Neither of us could get the spring-pin to hold through the handles despite much hammering, so I'm going to get a narrow and long bolt and nut per handle to secure them.
Seems a bit rocky because the upright height-adj. tubes are too loose in their supports, but otherwise OK. There are more holes for the positioning wedges on the wooden top than on my Black & Decker Workmate, and they have a concave side to clamp things vertically. And the height goes to huge, so that should be very useful!

Confusion

Hmm - confusion, methinks.

According to http://www.reprap.org/bin/view/Main/McWire_Cartesian_Bot_1_2 the x-thread is 19 ", y 11 " and z 9 ".

Except under the bill of materials (BOM) section, where x is 24 ", y is 18 " and z is 12 ". These measurements are the ones I used to mark my threaded rods. Again, I have chosen the longer lengths because I can cut them down as necessary, but once cut too short you're stuck with it!

Markings continued

For all those of you who have to cut by hand or using hand-held tools, here is a plan of the markings on the MDF, trying to make best use of material.

The hashed area is not used - yet.

I marked it in pencil, and discovered you can use a rubber (eraser) to rub out on MDF if you're gentle.

For the threaded rods, I marked the lengths using masking tape on the waste side, so that is where I can clamp the rods for sawing.

GO! Tues 21st April

Well, nearly. I spent all morning building up the workbench, but haven't quite finished it yet. Seems to have a design (or pre-assembly) flaw, and also some holes need drilling to get them to line up.
I have marked up most of the pieces for sawing, though:

• u-shaped rails - two lengths at 21 ", four at 13 "
• threaded rods - one length at 24 ", one at 12 ", one at 18 "
• MDF - four rectangles of 8.5 " x 11 ", one at 24 " x 22 "

The last rectangle is to be the base, with a 24 " front. This is the length of the x-screw thread. The distance front to back allows for the 18 " y-screw thread, with some added clearance in front of and the length of the rear upright added on. This may turn out to be too big, but I can always cut it down, whereas I can't grow it!

I warn you now, this is going to be a nice little mix of metric and imperial - just like the UK!

OK, that went relatively well - my longest wait was for a member of staff to come to my help, rather than when I ordered the taxi!
The chap who got me a trolley also loaded it from various aisles for me, wheeled it to and through the tills and outside ready for the taxi. I had to laugh because he picked a rubbish trolley with a jammed wheel! A whole wealth of tools and equipment on hand, and no fixing done there!

Itemised shopping list so far, including earlier purchases:

B&Q sub-total = £57.47

• u-shaped clamps = 15 mm saddle clips, pack of 10, £2.18 - not on their website, (aka pipe clips) - guessing the size required, but it won't break the bank if I've got it wrong.
• threaded rods, 8 mm x 1 m, part no. each £2.02, x2
• aluminium angles = raw aluminium corner, 3.5 cm x 3.5 cm x 2 m, part no. 3232630508305, £13.41
• aluminium u-shape rails = anodised aluminium U, 2 cm x 2 cm x 1 m, part no. 3232630214756, each £7.94 , x 3
• acrylic = OK, it's MDF, 6 mm x 1220 mm x 607 mm, part no. 5022652550011, £5.48
• flange = aluminium furniture leg, square profile, part no. 5013144016191, £5.48 (furniture leg)
• bolts for flange = machine screws, pack of 10, 5 mm x 5 cm, part no. 5020789853487, £3.06 (aka countersunk bolts and nuts)

Maplin sub-total = £2.99

• 4 " springs = 150 pc spring set, part no. , £2.99 - a box of extension springs (and others), hoping to be able to select correct sizes as appropriate.

eBay UK sub-total = £12.26

• Teflon strips = PTFE sheet, 3 mm thick, 10 cm x 22 cm, £6.28 inc P&P, from seller: gfgplasticfabricationsltd
• roller bearings = PTFE rod, 25 mm diam x 22 cm, £5.98 inc P&P from seller: bunaday - this item to be cut into rounds

I also bought a new workbench because our existing one is too short for tallish people like us. I hope it's good enough, it is B&Q own brand, part no. 5050451, £29.98. We needed this anyway, so I'm not including this in costings for the project. I'm also not including (for your purposes) the taxi fare home £5.

Running total = £72.72

Crutches

Being on crutches, I looked up all my large items online - only to find that none of my suppliers have these parts available to order online. So I rang B&Q to ask if I can get someone to load my trolley for me (too big for me) and to take it to the checkout. I rang my local taxi company to make sure I could get my 4 foot x 2 foot piece of board home, as I don't drive.
Everyone says no problem, so I get to find out later today.

See? still learning
My details already have the y threaded rod at 18 "....

And my MDF base will need to be thick enough to ensure the overhanging x motor clears the floor, or perhaps I can use little feet to raise the bed off the floor.

Learning

Things I've learnt so far

• Use 15 " y-axis threaded rod instead of 13 ". (Ref: BodgeIt) Not sure why, but happy to go with 15 " - can always shorten it, but couldn't lengthen it!
• Use 8 mm threaded rod instead of 6 mm so it won't bend so easily. (Ref: BodgeIt)
• Don't buy the screws as listed for the McWire (ref: PeterG) - fair enough, I shall figure out what size/length I need as I go along. (UK seller Screwfix is only a walk up the road.)
• Don't buy the springs until you determine what lengths are actually needed given the placement of pre-ordered x, y, z plates (called stages). OK, what I'm planning is getting some springs, and then placing holes appropriately. No holes will be in the same place anyway due to design alterations (eg MDF baseboard, no piping, flange, etc)
• Don't expect anything to go smoothly - it won't!

And don't try to get your straightness-checked 1 m lengths of threaded rod in a rucksack on your back onto the bus.

I hope I remember to make all the necessary alterations in sizes of nuts etc to account for all of the above.....chances?

Nope, thought not.

FAITH - the CopyCat Bot

How It All Started - a brief (ie 4 day) history

Wednesday 15th April 2009
Thinking about buying a plastics printer, and looking again at the RapMan. It doesn’t seem much different from the latest Darwin, and costs are reasonable, but…

Thursday 16th
…..looking at Darwin development, and the RepRap site with its “How to build a ….” reprap or a repstrap……. “I just wonder if….”
I hadn’t heard of the Repstrap, so I followed the link and was fascinated….

Lots of research about what may be doable – well the site does say it should be buildable by someone with "no special knowledge or expertise"…. well, that's me!

Friday 17th
The more I look into it, the more I want to build my own and have opted for the McWire (http://www.reprap.org/bin/view/Main/McWire_Cartesian_Bot_1_2) because it appears to have the most comprehensive pictures/instructions and hints. By Friday evening I’m hooked, and I’ve posted on the RepRap builders’ forum.

Saturday 18th
Research: it wasn’t easy to find the steel plumbing pipe in the UK, so I looked for alternatives.

I stumbled across the Wiki for the Lego reprap and the Fisher Technik one – WOW! I also kept on reading about other’s versions and problems and solutions.

Some people had used solid bases instead of plumbing pipe.
Advantage: no skewing
Disadvantage: lack of clearance below moving parts.
Plan: use a wide u-shaped solid base.

I also read that getting the holes in the right places wasn’t as easy as it should be, given that you can print off diagrams to tape onto parts in order to locate those holes. This was when I decided to use MDF for the x,y,z stages instead of expensive, and breakable acrylic.

Then what to use for the upright? Small sections of timber, propped with triangular support blocks.

Then how to hold up the upright known as “vertical base” without the plumbing pipe and flange? Hmm.

I’m spending a lot of time thinking about the plans, by now, so I added my marker to the RepRap map.

Sunday 18th
After a night of thinking about it, I had an idea of using a furniture leg with its attachment plate instead of the flange.
After a little scouting round B&Q, I found the perfect answer: a square-profile, hollow leg with plate with pre-drilled holes. Not expensive either, and fits smaller screws than the bolts required for the plumbing flange, thereby negating the need for really thick material for the vertical base. At least I think that’s why that sheet is thicker than all of the others. Time will tell when I start to put this thing together.

OK, committed now – having bought (some of) the bits, SHE’S OFF!