Making dogbones on CNC

 Here's hoping everyone has a healthy and successful 2022!!! 

Obviously this blog is about my teardrop trailer build, so I won't delve into opinions on beer, people, politics, life, etc - you can catch that over in ¨Life in the swamp¨ if you are interested.  Progress has been kinda slow for the past week.  I have actually had to pull some extra hours at my day job, and that's been enough to occupy most of my time.  In my free time, I've been clearing out the build space, and working on learning how to use the Path workbench in FreeCAD. 

Let's talk a little bit about FreeCAD.  There are other packages that are probably easier to use for generating gcode, like Fusion360 and V-Carve in particular.  Our makerspace/shop has a license for both, and I was starting to learn F-360 when the pandemic hit. At that point, I lost direct access to the machines (makerspace was closed down tight), and the F-360 personal use license was becoming 'difficult'.  Oh, and I built a CAD workstation using Linux, and F-360 only runs under Windows, so - not gonna happen.  Looking at the options, I started investigating FreeCAD, and found it was a)very similar to F-360 in capabilities (and difficulties), b)runs great on Ubuntu Linux, and c)it's really and truly free!  Not a demo license or one that allows you to create but not save, etc.  This is really free, is moderately well documented (good, not great) and has a very active user community, and numerous Youtube communities.

FreeCAD is a 3 dimensional parametric modeling application, with multiple workbenches supporting things like architecture, sheet metal, metal tubing, and 3D printing/CAM/CNC.  

OK, now the bad news.  It's a pain in the ass to learn, crashes occasionally, and many of the videos make assumptions about your existing skills that may or may not be appropriate.  And, while the documentation is often marginal.  If your last drafting experience was paper, ruler, t-square and a compass, it's a complete and total mind warp.  And if you are an 'experiential learner', your brain _will_ hurt - often.  If I paid myself $10/hour for watching FreeCAD youtube videos, I could probably afford a nice windows machine and full pro license for FreeCAD or V Carve!!!

But, I've gotten pretty proficient, made enough 3D widgets and sketches that learning one more bench wasn't that tough.  Even if that one drives a 10K spindle and can destroy 160 bucks worth of plywood in the blink of an eye.  

After a couple of false starts, today was the first day I've cut anything meaningful on the CNC.  It doesn't look like much, but these are the major components of a CNC job - perimeter profiles, grooves and pockets.  The 'dogbone' cutout was the most interesting challenge.  If you work in wood, you've doubtless learned that you can't put a 1/2¨ board in a 1/2¨ rabbet.  It won't fit (without some sanding/chiseling anyway).  Getting a shape like the dogbone to fit is even more of a challenge.  

To make it work, I used a .250 (1/4¨) end mill on the slot, and used the same mill on the tab - but told the program that it was a .240.  This positioned it just a little closer to the edge line, and allowed it to fit very snugly.  I am not sure I could get 10 of these in a row to fit like this though! Nor would the joint contain much glue. For the wall and ceiling seams, I will (after more experimentation) use the same technique, but make it .220 or .230.

And why am I so wrapped up on this particular feature?  Aside from the mechanics of making it work, I think it will be a nice feature on the inner sidewalls of the trailer, and the ceiling.  Having two pieces of plywood simply butt against each other is not the most attractive, and they tend to 'work' against each other over time. You can cover it with trim, or use a scarf joint to make it blend better.  Using puzzle joint means that the two pieces can't move freely, there's more glue seam, and glass tape with epoxy on the back will lock it in for good.  Note: in thicker wood, biscuits, shims or dominos will make a strong mechanical joint.

At the end of the day, I'm a definite fan of FreeCAD, and strongly support the direction that it seems to be going.  It is probably a lot more difficult to work with than a program like SketchUp, but the price is right, and the end result is spot on.  

Suppliers

 It seems like a worthwhile idea to keep track of the suppliers for this build.  I'll add to this as I go along.

Steel

COREMARK METALS
216 27th Ave. N
Minneapolis, MN 55411

612.522.5956

https://www.coremarkmetals.com/

steel tube, gussets, angle iron, aluminum diamond plate

Powder Coat complete

 Have to do a bit of garage rearranging, and get a kerosene heater to heat the garage, but we're making progress here!  The frame came back from the powder coat shop today.  Now it'll sit out in the weather for the next 72 hours while I wrap up re-organizing the garage, and pick up a kerosene heater to heat my barely above freezing in the winter space.  In the meantime, I continue to work on details on the CAD side of things - refining details, and [over]thinking details like panel joinery.  

I was finally able to find a local supplier for aluminum skis for the outside - I know I'm a few weeks out on that little effort, but I did not want to be sitting around waiting for them to arrive - so I pulled the trigger and ordered them.  I'll also order a sheet of diamondplate for the lower extremities, but that can wait - plenty of places to get it.

The frame came out great.  The welds look solid - not professional, but solid, and it's square within 1/16 inch on both the frame, and the axles.  I can live with that I think.

The tongue box frame was something I decided to go a little big on, knowing that it will never hold much weight.  It will contain a porta-potty in one end, the portable propane shower, and jack-stands.  I may yet change my mind on those, but at present I plan to use the wind-up style stands on the back corners.

Now it's time to flip it upside down, assemble the suspension, lube up the bearings and bolt on the wheels.  And then build the base...

And a quick shout out to Marco Sandblasting and Twin City Metalseal. They both did great work, easy to work with, and quick turn-around.  

Blasted frame...

Actually, it's _sand_ blasted frame!  It's grey, mighty grey.  The welds all look OK, no cracks, no warps.  By Friday it'll be very black. @MarcoSandblastingCo - Minneapolis

Draft look at the camper!!!

The frame is ready to go to powder coat, even if I wasn't!  I'll try to get pics from that step of the process, but - I really doubt that will happen...  It's been cold and snowy enough to keep me from wanting to load up the utility trailer, so hopefully tomorrow!

In the meantime, I've been spending time working in FreeCAD sketching out the camper. FreeCAD makes some tasks much easier - like taking 38.1mm off the outer profile to form the core of the walls, but managing all the constraints, attachment offsets and keeping everything in line is a royal pain.  I know about a 10th of the things I probably should, and am doubtlessly doing this the hard way - but hey - that's how I learn.  As the line goes in one of my favorite songs, ¨...if you came by it easy, you wouldn't be you.¨

Anyway, here are a couple of sketches/assemblies:

The outer profile has changed a bit from my first sketches  I decided I wasn't thrilled with the vertical lines front and rear, and since I was already beyond a convenient 8 sheet of wood, it didn't really matter if it ran a little long.  So the back and front arcs make it closer to 10'3''.  It's amazing what that couple of inches adds to the look.

The bed area is queen size - 58Wx78Lx6H.  The cupboard on the center wall is intended to be hanging locker on one side, and shelves on the other.  Should be plenty of room.

I truly don't remember whose video/build journal I saw with the headboard, but I had to steal that idea.  It's about 4¨ at the top, and 6¨ at the bottom.  It'll grow shelves, and be set up for a tongue mounted AC unit blowing in from the top.  The 10 degree angle is pretty comfy for leaning against to read or watch videos.

Behind the wall is the mechanical/electrical bay.  It's sized for a Propex 2211 on one side, and a 200AH battery system on the other.  

I'd still like to install a 20 gallon belly tank, but at this point I will go with the big blue jug out back, and another stored in the tow vehicle for shower water if we're off-grid.   

The kitchen is still a work in progress.  Mostly, I am leaning toward a fairly spartan - and flexible - arrangement since I don't know what I will really like, need, or want.  The bottom space is sufficient for a 55l fridge on one side, and a water jug + drawers on the other.  I'll have a Camp Chef Everest on a slide out, probably on the left side.  There will also be some sort of containment system at the back of the counter to hold 'stuff'.  

That's a really quick tour, and at least a glimpse of where my head is at.  The amount of learning I've done from the tnttt and youtube communities is incredible.  I've changed or tweaked so many things already based on videos or posts from fellow builders, and I appreciate everyone who has put their thoughts out there!

Ready for powder coating!

 It was a boring day.  Boring holes in the frame, that is :)

My buddy Kris came down and helped me get the frame down on the blocks, double check alignment, clamp the suspension,  mark the holes, check the alignment again, and then drill the holes.  And I have to confess that I can't drill a straight thru hole to save my life.  I'm going to find a way to get at least a couple of them a little off center.  But at the end of the day, I thin we are 'close enough'.  Triangulating spindle to tongue is within 1/32 of an inch.  I'll get it professionally aligned once everything is together, and the body weight is on the frame, but this will do for now - especially when it will be taken apart again.

Assembled Timbren suspension units in place!  These are definitely heavy duty!  Grade 8 bolts thru the  frame.   i had a little sticker shock when I bought nuts, bolts, and washers.

The Timbren specd reinforcement plates fit well.  Only a little nudging was needed to get them properly aligned.  

One 'sticker shock' item for me was the bill for Grade 8 hardware!  Bolts for both the suspension and the receiver were nearly $100.  That's the price for doing it right.

Final inspection tomorrow, and off to the powder coaters on Monday!

Done welding?

 And it's a complete frame!

Today was a really big day.  I finished welding up the last couple of welds, added the tongue box frame, and the bike rack post.  It's probably over-engineered, but I think the welds are solid, and the design is good.  

A couple of things I decided not to do:

Bash guards on the sides of the trailer.  Originally, I'd thought about adding bash guards to protect the fenders if I got too close to a tree or whatever.  But this isn't going to be an off-road trailer, so extra weight, extra work. 

I'm also planning to omit the rear hitch.  I could still change my mind, but to what end?  I will have a bike rack over the tongue box, so the only real reason for it would be an extra bike, or a tray.  I'm open to opinions, but I have to decide by Sunday - Monday I have a date with the sandblaster and powder coater.

Before I could weld it on, I had to modify the rack mount post.  It's slotted to fit over the frame tube which took an excursion into the machine shop to mill out the sides.  This is an older mill, positioned by hand.  I haven't run a Bridgeport in a couple of years, and it took some time to remember which way to turn the cranks, how much to remove in a pass, etc.  Only a few little oops moments, none of any importance.  Besides - the welds would cover up any sins!

 Bike rack receiver installed.  Welds at the bottom deliberately omitted so that water can run through!

Since a couple of people have asked about an earlier comment that I would 3D print end-plugs, here's a sample.  I had a roll of TPU already in the printer, so I did a quick proof of concept last night, and printed one this morning.  I'll refine this a bit - chamfer/radius the top edge, and make a version with a hole for a clearance lights.  

They can be made in a variety of sizes to match a variety of tubes.

I'll make these available for sale later. PM me if interested.

That's all for today.  Next up - mounting the Timbren and reaching 'done'!

It always takes longer than you planned...

 Well, there's always something else that has to get done.  After losing a couple of days last week due to a COVID concern at the shop and the holidays, I'm finding that cleaning up welds takes more time to fix than the original welds did.  My end result is OK, but the process to get there is time consuming and more than a little warm!  (Tonight's lesson - don't sit where you just welded...)

Cutting the 'wings' for the tongue was interesting.  It's roughly a 24/66 degree cut - roughly.  However, most stationary tools can only support a 45 degree cut.  We opened the bandsaw throat a little wider, positioned the tube on the cut line, and clamped it down with C-clamps and cut that very acute angle.  It was 'close enough' that a little work with a flap wheel brought it into spec.  

I've still got to add the frame for the tongue box, the rear coupler, and run thru one more quality check to clean up any really ugly welds (the things you find in the bright light of day!).  

Next big task is to drill the Timbren mounts, add the bike mount post, and then it's off to the powder coater.

One thing I'm pleased about is the the frame came out pretty square (so far).  Tip of the tongue to back corners is within 1/16 of an inch, and it seems to be within 1/8¨ for flatness.  I think I got a little lucky on that - I realized that even with alignment corners, I should have clamped each bar for both horizontal and vertical axes.  I only clamped the long rails horizontally and the cross bars on the vertical.  Sometimes it's better to be lucky than good?