Let's talk / Getting Started

Good news! I've got a friend locally who has access to an FDM machine. He's not familiar with the Mendel but I sent him some info and he may be able to make me a set of Mendel parts. If so, we might be able to start with a Mendel instead of a MakerBot and save that cost.

That may be expensive. ~1000USD in plastic (printer cartridge business model). Compare the cost to building a RepStrap or buying a used desktop milling machine/CNC router.

I know nothing about FDM so I have no idea what the costs are. I'll post when I find out more.

Your friend's workplace will probably be paying ~USD6 to 10/cubic inch for the plastic.

Mendel is about 67.6 cubic inches of plastic:
[objects.reprap.org]

So you're looking at a build cost of USD406 to 676 just for the plastic.

Well, it looks like I may have a set of RP Mendel parts early next week from my friend's FDM machine. I still need to get the electronics and other mechanical parts but that gets me well down the road. I don't know how much trouble I'll have getting a Mendel up and printing or how quickly that can happen but I'm willing to help get more local people fixed up with RP parts.

SheepdogRD, you were sort of spearheading the collaboration that we were talking about. Want to help me get some mechanical parts and get this sucker rolling or are you still inclined to go the MakerBot route?

Rob.

I've pulled back on the MakerBot idea. We've pretty well decided to go on and build a RepStrap of our own design, which will print RepRap parts. We'll need many of the same parts you will, and perhaps we can grab the SPSU students and order with them. I put together a spreadsheet that tells me how many boxes of each fastener to order depending on the number of RepRaps being built.

I've also seen that the advantage to group buying is primarily in fasteners. There's no significant savings in rod or bar.

We go by McMaster-Carr every day, and we have an account there, so I'd be happy to get the parts and divvy them up among us. I'll work on finishing the parts-to-order list.

The Mendel electronics are available here: http://store.makerbot.com/generation-3-electronics-mostly-assembled.html.

Yep, I ordered the gen 3 electronics, a spool of black ABS, and some nichrome wire from their store earlier today. Just let me know how much the parts are per person and when to be where to help divvy them up.

While I'm thinking about it, any further thoughts on metric versus imperial? We'd all prefer cheaper parts, I'm sure, but it's hard for me to guess at how much the difference would matter without seeing how much play there is in person.

Rob.

We've pretty well decided to go on and build a RepStrap of our own design, which will print RepRap parts.

If it's novel or fun or useful, please wiki it up as you go along. We need to build up a bestiary of RepStraps for our user/builders.

(Edit: That's if you're blogging it anyway.)

Edited 1 time(s). Last edit at 01/08/2010 08:40PM by SebastienBailard.

I'd rather build using the imperial parts. On this side of the pond, imperial parts are generally less expensive. An extreme example is the threaded rod. Zinc-plated threaded rod in M8-1.25 x 1m is $11.00 at McMaster-Carr, but 3/16-18 x 36-inch zinc-plated threaded rods are $2.27. It appears the net difference is around $60 per RepRap.

For those building RepRaps, it may be worth the difference to stay metric, right in line with other units being built internationally. For our RepStrap, we'll likely go with inch fasteners, because we're using a differnt deck completely, and the parts we're using are inch-based. I agree with your impressions, Rob; from what I've seen, we might be able to use the same printed parts whether we use imperial or metric fasteners; there are only tiny dimensional differences between metric and equivalent inch parts.

In my calculations, I left the M8 rod and bearings in the imperial unit build because 5/16" ground rod is significantly more expensive, and I saw no benefit to switching.

Edited 2 time(s). Last edit at 01/09/2010 09:17PM by SheepdogRD.

I've added to the depth of the spreadsheet, and done some more calculations on group buying. The primary group buying advantage is in the fasteners that generally come in boxes of 100. The difference is in the leftovers -- parts beyond what the build list calls for. For example, the build calls for 54 of the M4 x 40mm cap screws. A solo builder has to spring for a box of 100 fasteners, and has 46 left over, where a group of 5 buys 3 boxes of 100 and ends up with 300, or 60 each, meaning there are only 6 extras per builder. Overall, a lone builder has over $40 worth of leftover fasteners, but that number shrinks to less than $4 per builder in a group of 5.

Beyond fasteners, most other parts can be purchased individually, because there's little advantage in group buying other than reduced shipping costs. MakerBot allows a 5% savings for a group of 5; that would save $8.75 per builder, and it would reduce shipping expense.

Here's how the cost breaks out for the metric parts -- just the capscrews, washers, nuts (both hex and Nylok) and the threaded rod:
1 unit @ $185
2 units @ $162
3 units @ $155
4 units @ $152
5 units @ $149

With more than 5 in the group, the additional savings are insignificant. I included the threaded rod because it goes with the choice to use metric fasteners and affects the overall cost of the build, even though there are no savings in buying it as a group (because it comes in individual lengths, not multiples).

Using imperial fasteners in a group of 5 cuts the fastener cost nearly in half. I substituted 5-40 fasteners for M3, 8-32 for M4, and 5/16-18 for M8. For the same parts -- capscrews, washers and nuts (both hex and Nylok) and threaded rod -- imperial parts cost less:
1 unit @ $107
2 units @ $86
3 units @ $81
4 units @ $80
5 units @ $75

Once again, with more than 5 in the group, the additional savings are insignificant.

As I posted earlier, I calculated costs using the M8 rod and bearings in the both builds because the diameters are so close that units can use either type. McMaster-Carr sells M8 ground rod only in unfinished steel, and it sells 5/16" ground rod only in stainless steel. Using stainless steel effectively eliminates the likelihood of corrosion, but stainless steel increases the parts cost about $81 per unit. Steel choice is a decision each builder can make, because those rods can be ordered either way without affecting the cost for the group.

Here's a link to the Google Docs spreadsheet I used:

https://spreadsheets.google.com/ccc?key=0AiYeuHn2-JgJdEtfQ0pFNjlueko5UWE3Rm5pMmxMbUE&hl=en

If someone would check the part numbers to see if you concur, I'd appreciate it.

Who's in?

I'm in.

We all have to agree on imperial or metric for the fasteners (and threaded rod), right? There doesn't seem to be a particular need to stick with metric for those and imperial is significantly cheaper so I vote for imperial.

Your spreadsheet only has 'total cost' sums for all-metric and all-imperial but also mentions each builder choosing their rod type. Those who are trying to keep their costs down could go with the imperial fasteners and metric rods and we don't expect problems, right? Total cost on that would be ~$180. Is there anywhere else to get rod from locally where we may have more options for the type of steel?

I know that I'm probably rushing things a bit but I'm hoping that we can get commitments and an order in pretty soon. I'm anxious to get building.

Thanks for trying to get this organized.
Rob.

Ignore this post. Nothing to see here. Please move along.

Edited 1 time(s). Last edit at 01/12/2010 06:11PM by robsweet.

I've revised the spreadsheet to add explanation and lay the costs out more clearly.

I've also emailed the SPSU students to see if they're interested.

Edited 1 time(s). Last edit at 01/12/2010 06:51PM by SheepdogRD.

There are more revisions on the spreadsheet, to bring it in line with the Mendel assembly data sheet. I added the extruder-specific cap screws on both metric and imperial builds.

I also did a recalculation on the metric threaded stock; you can see those calculations in the second sheet of the spreadsheet. Because the M8 threaded stock from McMaster-Carr is 1.2m long, instead of 1m, the cutting can be much more efficient, and I was able to reduce the number of bars required from 9 to 6. That cut $33 off the metric build cost.

The new costs are reflected in the spreadsheet linked above. You'll see that the difference between equivalent metric and imperial units is now down to about $40.

Edited 1 time(s). Last edit at 01/13/2010 08:50PM by SheepdogRD.

I think I'm inclined to go with the cheapest option. I'm not wild about the unfinished steel but I'm more confident that things will work properly with metric rods. As we don't think that the imperial parts will matter for the rest, I figure that we might as well save the $40.

So we've got two with you and I. Anybody else on board?

Rob.

Hi guys, sorry I haven't talked in a while been covered up.

I recommend ground a2 tool steel for the bearing rod(I think Vik directed me) it is what I have on my mendel and seems to be good stuff
8116K7 A2 TOOL STEEL TIGHT-TOLERANCE METRIC ROD, 8 MM DIAMETER, 3' LENGTH 13.02

The part number in the spreadsheet for 8mm threaded is for nuts, so I included the threaded I used for reference.
94185A160 METRIC TYPE 316 STAINLESS STEEL THREADED ROD, M8 SIZE, 1-METER LENGTH, 1.25MM PITCH 11.38

The part numbers are McMaster. Hope this is more help than hindrance.

Thanks, Johnny -- I appreciate the checking you did. Using the part numbers you suggest makes a big difference. I've further revised the spreadsheet.

I also used less expensive bearings (the RepRap Materials Procurement notes say this: "Mendel does not impart big loads on any of the bearings, therefore high specification bearings are not at all needed. Get the cheapest ones you can"). I suspect even lower-cost bearings are available.

The new part numbers show that changing the metric unit to stainless threaded rods adds only $9 to the cost, so that seems a worthwhile shift, but changing the imperial unit to stainless threaded rods adds a whopping $100, taking the cost of the imperial unit above that of the metric one. The ground rod is also available in stainless for imperial units, but that adds another $144.

I don't think using metric or imperial rods will make a difference; they're less than .003" apart in diameter, and they're just tracks for the bearings to roll on.

So, we have two buyers for imperial parts. That size group puts the kit at $127. A group of 3 makes it $124, 4 makes it $119, and 5 makes it $116.

Who else is in?

Edited 1 time(s). Last edit at 01/14/2010 12:37AM by SheepdogRD.

You may also want to check vxb.com for the bearings. I bought my 624s for $1 each from them, with 48 to a kit they add up quick. I'm not sure what size you will use on the 8-32 bolts, but vxb's homepage shows your inside diameter options.

By the way good work on the spreadsheet SheepDog, that was no 5 minute job. I am sure that there are other people out there that could make use of these conversions. You may want to post a link to your spreadsheet in the general forum or somewhere that more people read.

I checked out vxb.com, and they do have good prices. They also sell through Amazon, which is a confidence builder. They're now the bearing supplier on the spreadsheet.

I'm glad you mentioned the other bearings, Johnny, because I'd forgotten about them, and they change things a whole lot.

Looking for bearings has really thrown a fly into the ointment in the "imperial" measurements effort. I've been looking for an imperial equivalent for the metric 624 bearing, which is 4x13x5mm and is used on the 4mm cap screws. By my calculations, the 4mm inside diameter is 0.157", very close to 5/32", which is 0.156". Sadly, there are no machine screws with a 5/32" diameter; that dimension falls between #6 (.138") and #8 (.164"). Unfortunately -- and here's one of the places where the imperial fastener system shows its inherent screwiness -- bearings are made for shafts in 1/32" diameter increments, but fasteners don't come in 1/32" increments below 1/4". Doh!

(If this is unfamiliar territory, here's a good place to review thread sizes in the imperial system: http://www.engineersedge.com/screw_threads_chart.htm)

In reality, that probably doesn't present a problem, much of the time. Higher speed applications would require putting the bearings on shoulder bolts. Putting bearings on threaded rod is non-standard; it's fine for low-speed applications like this one, but I don't think it's a good design practice. In small imperial fasteners, it just can't be easily done because of the dimension mis-match.

We can get machine screws that come pretty close to the metric size, but no bearings to run on them, or we can get bearings that come pretty close to the metric size, but no fasteners to support them. I even explored shoulder bolts, but they don't have enough threaded length to work for us. I considered using sleeves and choosing bearings with a larger inside diameter, and I'm working on that as a side project. So far, it comes to the same imperial system problem: sleeves, like bearings, have I.D. in inch dimensions, but fasteners are in the numbered series up to 1/4". Grrrrrr . . .

To keep the spreadsheet going, I wanted to keep costs comparisons on a comparable footing, so I guessed that imperial bearings will be the same cost as metric ones -- if we can find something that works. I'm not ready to stand up and swear that we can make imperial parts work, yet. Maybe I'm missing something; I'd love some suggestions.

I suppose the printed parts can be drilled, but that shifts the approach from printed parts that fit universally to parts that fit metric builds and can be modified for imperial builds, or to separate printed parts for each kind of build. I was hoping there would be no need to modify the parts when we use imperial fasteners.

As a result, I'm ready to bite the bullet and use metric parts, for several reasons: (1) the difference is down to only $40; (2) I can eliminate over half the difference by choosing 5/16" ground stainless rod instead of M8, because there's a diameter difference of only .003"; (3) I'd get stainless steel rods instead of plain steel; (4) I won't need to worry about recalibrating the Z axis from metric threads to imperial threads; and (5) I'd be helping move the USA to the metric system by increasing the volume of metric parts sold here.

Rob and Robsweet, you've already voted for the imperial parts. How does that sit with you? Would you be willing to switch? If so, I'll join, and we'll have a group of 3. If not, do you have any suggestions on how we get through the bearing impasse?

Edited 1 time(s). Last edit at 01/17/2010 10:54PM by SheepdogRD.

Rob == RobSweet

Yes, I'm willing to switch. I've got to make arrangements to pick up my printed pieces (sometime this week) but I've got my electronics and most of the other odds and ends so I'm mostly waiting on the rod and fasteners to get this show on the road.

Ah, you Robs are one, not two. I didn't want to make that assumption, but now I get your comment about "Ignore this post. Nothing to see here. Please move along."

I still have no answer from the SPSU folks.

I did yet another Google search for zinc plated threaded rod, and decided to investigate the advertisers on the search; I found fastenermart.com, with good prices; shipping is unknown, but I'll find out today. If we guess shipping eats up $40 or so, and choose to go with the 5/16" stainless ground rod, we've gotten the cost down so there's almost no price penalty for metric parts, and the parts are all zinc plated or stainless.

I've done another refresh of the spreadsheet. I think I'll pretty much ignore the imperial portion of it, henceforth. Unless someone objects, I think I'll archive that section and cut it off the working spreadsheet. In fact, I suspect it's time to add the metric information to the RepRap "Mendel-M4-assembly-data-sheet.ods".

Despite the fact that there are only two of us, I'm ready to place an order. I'll get shipping costs today and add them to the sheet, and we should be ready to order tomorrow.

The spreadsheet is updated. We're getting down to some pretty good numbers, here. Although the total shipping cost from fastenermart.com is an unknown, I left it at the single-shipment price. Another shipment would add as much as $6 per build; if they quote any higher than that, I'll just return to picking up the fasteners at McMaster-Carr.

Including shipping, the metric unit is currently about $141 in a group of 5, $146 in a group of 4, $154 in a group of 3, $167 in a group of 2, or $217 all alone.

We have 2 -- anyone else ready to go?

If you're not ready yet, but will be soon, what's your time frame?

Shipping costs are in, and the costs remain unchanged from the last post: about $141 in a group of 5, $146 in a group of 4, $154 in a group of 3, $167 in a group of 2, or $217 all alone.

Oops -- I've corrected the spreadsheet to reflect the proper screws from FastenerMart. Somehow, I included the part numbers for zinc hex-head screws instead of black socket-head screws. The price increased about $8, but we're still under $150 in a group of 5.

I live in Winston-Salem NC, but have family in Atlanta. I am interested in going in with you for the hardware. I don't read your thread often, so please PM me when you order, I will likely throw in

---

repraplogphase.blogspot.com

Hey all.

New to this whole Reprap thing, but also (may have) an interest in going in on a group buy of hardware. Located in Huntsville, AL, so not too far away, either.

I know some of the early discussion dealt with a ramp-up program to begin producing the initial parts, and then hope it catches like fire from there such that everyone can get a set. Is this an update on that? I'm very interested in getting started, but am weary to holding on to a box of hardware with a group of people hurting for the printed parts to go further.

I will attempt to contact some of my old friends still in school (many of whom work in the campus machine shops) regarding the possibility of getting some cheap components printed on one of their RP machines or machined of aluminum on one of the mills.

Cheers,
Joel

I think our orders were placed last week but there are at least two of you interested in ordering more parts. I'd see if you could get one or two more people and use Sheepdog's info to do your ordering.

Good luck.
Rob.

Hang in there -- I'm helping Johnny set up to carry kits in his store at ultimachine.com. Give us a week or so.

Well, that's good news for everybody. Thanks!

Printed parts are still pretty hard to come by, but people are working on that. As more RepRaps get built, more parts will be available.

For now, CNC milled parts may be a very good alternative. You might look to your friends with machine access to produce the the larger parts; those appear to be the most difficult and time-consuming to produce. Then see if you can find the smaller, easier pieces available in the RepRap forums.

Please see the new thread in this group covering a meetup on February 20.