CNC Design

[capnTelescope]

Video is up!



Includes a tour of the machine and the actual drawing on the plywood. I also left in a couple of "oops-es" for comic relief. I had a couple of problems related to my not usually going to the extremes on the axes.

It ain't purty, but it's real.

[aggie79]

Welcome Captain T!

Glad to have another teardropper from the great state on board. Be sure to check out the South Central section for area gatherings.

Strength and light weight are the main goals. I haven't seen even one builder complain that their Tear wasn't heavy enough. I also want to minimize the amount of left-over dead tree.

Most designs have a number of subcomponents that are added after some initial assembly. Most notably, bulkheads, the cabinetry in the cabin and galley. My design makes these an integral part of the structure, adding strength while adding minimal extra weight.

I can't claim that my teardrop is "light weight" - I haven't had it weighed - but you're spot on in that the different assemblies contribute to the structure. The picture below is the interior side of my teardrop. I cut dados for the bulkhead framing, and headboard face frame and shelf, and a rabbett for the floor. (The rabbett is extra wide because my sidewall overhangs the frame rail and I wanted to leave some space between the frame rail and sidewall.)



This is a picture of the walls and floor and framing together.



Even without the exterior wall and roof skins the assembly is amazingly strong.

Also, we often make some compromises with good woodworking practices. Most notable here is the common way of installing bulkheads and roof spars. Often, bulkheads are mounted by screws from the outside into the edges of the bulkhead plywood. This has several disadvantages. Most notably, screwing into end grain risks splitting the wood. It is less stronger than a screw through the face of the plywood. But IMHO the bulkheads can be one of the main sources of strength of the basic cabin assembly of floor, walls and bulkheads. Also, the through screws from the outside make extra work, as you usually see them countersunk and filled over and sanded. That's a lot of extra work. It also prevents you from skinning and trimming the walls until after assembly. When the walls are vertical, you have to fight gravity. So I want to skin the wall subassemblies on the workbench, before any assembly begins. I'm risking scratches and dings, so we'll see how that goes.

I don't know what exterior finish you plan on having, but take a look at Planovet's build: http://www.littleswissteardrop.com/buildpictures.html. Mark completed almost all of his interior and exterior finishes before assembling his teardrop.

Others have commented to your questions. Here are some miscellaneous thoughts I had on your design:

1. Depending upon your finishes, but 1/8" plywood inside and out will be plenty strong instead of the heavier 1/4" plywood.

2. Also 1/2" plywood could by used for the bulkhead framing instead of 3/4" plywood.

3. Before you cut the profile, you need to figure out how you are going to do your hatch. They fall into four categories - Steve Frederick method (this is what Planovet used), zero offset hurricane hinge, offset hurricane hinge, and "Len's method". The first three will require you to notch of cut your profile. I used the zero offset hurricane hinge, but the "zero offset" refers the the roofline being on the same plane for and aft of the hinge. Aft of the hinge, you need to notch the profile to allow for thickness of the overhanging roof skin(s) and weatherstripping. Here's a section showing what I'm talking about.



(Credit goes to Grant Whipp for the drawing.)

Here's chicken-scratching showing the notch in relation to the sidwall/hatch/framing:



I cut the notch with a router after the walls were up. Here's a picture showing the notch almost completed:



In Len's method, no notch or cut is required for the profile: http://www.tnttt.com/viewtopic.php?p=1045874#p1045874.

I can't wait to see this build get going!

Take care,
Tom

[mikeschn]

Video is up!



Includes a tour of the machine and the actual drawing on the plywood. I also left in a couple of "oops-es" for comic relief. I had a couple of problems related to my not usually going to the extremes on the axes.

It ain't purty, but it's real.

Nice video Brad...

Is your magic marker spring loaded?

Mike...

[capnTelescope]

Mike -- 100% pure natural certified organic Gravity. It helps a lot to have a newish marker with plenty of ink. The marker fits loosely in the holder and seems to do well with surface irregularities. If Plan A didn't work, I was going to add weight to the top end of the marker.

I tried pencils, ballpoint pens and profanity first, with a different holder design. This was the first time I used the marker method, and it worked pretty good, if I do say so myself. It won't do any precision drawing as is, but this exceeded expectations for what I wanted.

[MtnDon]

Pretty cool machine capn. My son is a machinist, CNC trained. I've coveted a woodworking CNC ever since I first saw him program and operate a CNC milling machine. Thanks for the video.

DonM

[capnTelescope]

Hi Tom, welcome to my humble thread and a hearty Class of '72 Howdy to you. I thought it was time for another Aggie to speak up.

I've been following your posts and Silver Beetle build for some time. You did a great job on your Tear!

I plan to skin my tear with sheet aluminum, probably .030 thick or less if I can find it in 4x10. I want a shiny one like you have.

I'm about to refer repeatedly to my "next build." I don't have a Next Build planned, but I'm pretty sure I'll want to take another crack at it someday.

1/2" Plywood -- If I find a source of quality 1/2 ply, maybe on the "next one." For this build, I wanted to use materials that are easy to find. I live within 5 miles of 2 Home Depots and a Lowe's and their 1/2" is ap-cray, but HD has some nice 3/4 from Chile.

1/8" on the walls -- I wish I weren't committed to 1-1/4" walls for my Vintage Tech's doors that are taking up half of my project staging ("dining") room. Diminishing returns sets in here. 3/4" is about 75#, so quarter inch must be about 25 # and 1/8" 12-13#. Maybe I'll look into Foamies for the Next Build. I am going to use 1/8 Baltic on the ceiling and the roof.

The Dreaded Hatch
I'm glad you asked that question. I'm planning to merrily head off into the tall grass, here (kinda like how I play golf).

While I look into Len's method, I'll leave everyone with a question to ponder:

What common household item closely resembles a teardrop hatch?

Answer tomorrow, PLUS how I plan to build my hatch. I haven't seen anything like it on this forum.

[capnTelescope]

Hi Don. Welcome to the thread.

I used to program NC machines for my daily bread, back in the mid-70's. This was back in the days of punched tape, ASR-33 teletypes, 110 baud rates and before they tacked the extra "C" in front of the "NC." And a quarter million dollars was some really serious money, that could buy 9 or 10 houses or a smallish NC lathe or mill. Having one of my own was an impossible dream, then. Fast forward to AlGore inventing the internet and people having personal websites, and some people are out there building their own CNC machines. I was hooked again. I'm having a blast playing with my router.

You owe it to yourself to get one, one day.

[aggie79]

Hi Tom, welcome to my humble thread and a hearty Class of '72 Howdy to you. I thought it was time for another Aggie to speak up.

I've been following your posts and Silver Beetle build for some time. You did a great job on your Tear!

Fantastic - another Aggie in the ranks! I'm class of 79, or at least that is what I should have been. I majored in bonfire construction, intramural sports and the Corps of Cadets. Even so, I managed to cram a 4-year degree into 5 years at ATM and 4 summer schools in between.

I plan to skin my tear with sheet aluminum, probably .030 thick or less if I can find it in 4x10. I want a shiny one like you have.

If you can't tell from my degree plan and the 3-1/2 years I took on my build, I prefer leisure over hard work. Polishing aluminum wasn't certainly going to be in my repetoire even though I wanted the look. Luckily I found the desired look and maintenance-free aspect in aluminum sheeting at a sign materials supplier. While not as bright as true polished aluminum, it is reflective enough and being anodized it stays that way. You may want to check suppliers that sell to sign-makers for a similar material.

The Dreaded Hatch
I'm glad you asked that question. I'm planning to merrily head off into the tall grass, here (kinda like how I play golf).

While I look into Len's method, I'll leave everyone with a question to ponder:

What common household item closely resembles a teardrop hatch?

Answer tomorrow, PLUS how I plan to build my hatch. I haven't seen anything like it on this forum.

I can't wait to find out - maybe a refrigerator door?

Gig'em,
Tom

[tony.latham]

Brad:

Thanks for posting that video. I'm jealous. Real jealous. So jealous that if I had an empty shop corner –and I don't– I'd be scheming.

Keep up the posts.

Tony

[capnTelescope]

I'm sure the suspense is just killing people...

Q: What common household item most closely resembles a galley hatch?
A: The trunk lid on your car.

But how often does your trunk leak? Hardly ever. If you read my intro, you'll remember that I spent some years as an automotive technician, otherwise known as a mechanic. So there I am, working away while puzzling how I want to design my Tear, and it hits me one day that the trunk lid is just like a galley hatch. Without a Hurricane Hinge. Can this be done on a Tear?

Here's where I'm going to wander off into the weeds, hopefully without getting lost. The trunk lid works by giving rainwater a flow channel and depends on the fairly reliable principle that water doesn't flow uphill. A gasket takes care of the rest. I'm thinking that the CNC will give me enough accuracy to make this work. (fingers crossed) Don't try this at home...

This sketch hopefully explains better what I'm getting at:



The seal I'm showing is Metro Molded Parts LP103B, available from metrommp.com. Not to scale. Gotta put my order in.

BTW, this is very similar to the Len Method mentioned above by Tom. The main difference from Len's Method is the gasket (shown in black) is on the bottom here, and seals what water is left at the very top. There is an interesting current thread titled Hatch Research at viewtopic.php?f=21&t=57849 that includes an interesting post by Len19070.

[capnTelescope]

Tom -- You must have been on the same degree track as me. 5 years & 2 summer schools. Graduated in August of 73, just in time to not start my sixth year. GPA rounded up to 2.1. I still have nightmares of having one more course so I can graduate. Majored in Beer, goofing off and wishing there were more ladies on campus (They were still scarce when I was there). The draft kept me going.

The shiny anodized aluminum sounds like just the ticket. I better start looking.

I keep having small details get in the way of making router dust. I can't do this or that because I don't have something in my hot little hands to measure for.

Gig 'em
Brad

[capnTelescope]

Tony -- I don't care if you're jealous, but please don't hate me.

Maybe it's time to build a lean-to next to the house?

[aggie79]

Okay Brad,

You threw me off a little bit with the household item reference. There was a build on here some years ago that incorporated the "trunk lid" design. Let me see if I can dust of the damage caused by the former Sparky's honky tonk in College Station and come up with that build link.

Take care,
Tom

[capnTelescope]

You do own a car? That you keep in or near the house?

It doesn't surprise me that someone tried it already. I haven't hardly ever had an original thought, but many times I thought I did.

I did some looking for bright (shiny) anodized aluminum and found 4x10 sheets for ~$125 plus shipping. That sound about right to you? They didn't say where they were. shipping could cost more than the metal. I also found a place in the DFW area: Wrisco Industries.

Also there is bright gold anodized. That would be different. I doubt anyone makes trim extrusions in that color, though. Drat.

Was Ralph's Pizza still there when you were? They did me some harm a time or two. I don't remember Sparky's. There's a couple of possible reasons why.

[capnTelescope]

@Mikescn -- you expressed interest in my marker holder. Here it is in excessive detail:


bottom/side view. made from a piece of scrap. The extraneous cuts aren't required.


Same diameter as router motor, thru hole a little larger than the marker


same as above. I needed to add an extension to get below z axis stuff.


Hole in the extension piece to allow the tip to peek through enough to write without dragging the holder. I had to continue the larger hole from above, then the small hole for the point. The marker should move freely in & out of the extension piece.


showing the gap around marker in the hole.

Your CNC wants to do this project.