Form block questions

[Texaspilot]

I am mentally preparing for a build and I had a few questions on the form blocks.

1) I’ve not seen or read about anyone bolting two pieces of mdf/hardwood together and bandsawing to get the master form block and a backup copy at once. Maybe this isn’t possible, most seem to use a router method. I am not highly experienced with power tools, so perhaps I am thinking wrongly. Can I do this?

2) For hammering the forms, does one normally use one full sized form with a radius, or make separate ones for nose center and rear sections?

3) For getting the 1/8” radius on the hammer block, is there a 1/8” radius router bit to accomplish this?

4) I built a crappy looking router table by bolting my plunge router to a piece of scrap plywood. It looks ugly, but appears to cut straight. Will this be adequate for my router work?

5)as an afterthought is there a router bit to make the undersized form that I will bolt to the hammering form?

thanks y’all

[way_up_north]

All power tools are dangerous please follow safety rules...

i suggest you you watch desert Bearhawks YouTube videos on this....I did mine differently ...but by watching his methods ...we can discuss the pros and cons of each method....

#1
the router trim bit makes a nearly exact copy of the original.....so make your wood form block...carefully sand it to the line....go nice and slow...you'll make a masterpiece of a block....then use that to trace out the second part....cut the second part out near the trace line...then bolt them together ...using a fostner bit to counter sink the bolt hole...so the bolt head is bellow the surface.....then take that to the router table...slowly and carefully router around the 2 blocks....you'll end up with matched pairs....the router trim bit can last a long time if you lube the top bearing and go slow....on long cuts I lube the bearing 2 or 3 times...go slow so the bit does not overheat....and check the bearing is tight between cuts...Allen key on top of the bearing is tight...



#5
yes you can do it that way.....but I prefer to make the blocks the same...then adjust the metal rib with the RV rib straitener tool....

[S Lathrop]

I used a piece of 1" thick hard maple for my form block. I took the Mylar drawing of the wing profile, had it printed and I glued that print to the form block. Saved a lot of layout time. I found that having the print on the form block was very handy. After making all the ribs, most of the drawing is still visible on the form block.

On the drawings for the ribs there are a few jig pin holes. I added other holes so that every rib type had 2 jig pin holes. The pins allow me to align the blanks for the ribs and were used to make the patterns for all the ribs. I used a hand router to cut the ribs, including the lightening holes. To cut a center rib took about 4 minutes, lightening holes included. I could cut 3 ribs at a time. It is a very messy job. with chips flying all around the place when you cut a rib.

[Chris In Milwaukee]

The problem with the "bandsaw together" option (at least with my bandsaw) is that the blade tended to wander and made for ugly form boards that needed a lot of attention. So I created a master from which I could create other form blocks (with a router) if one of them became damaged.

For the radius, I just eyeballed it and used a sanding block. The metal won't stick exactly with the form block while bending it. But it'll use it as a guide. If you want to check your work, though, take a small hunk o' metal, drill a 1/4" hole in it, and use your bandsaw to cut 1/4 of it off to the tangent of the drilled hole (like taking 1/4 of a piece of pie out of a tin). You can run that up against your sanded edge to see how close you are.

2019-08-26_10-08-55.png

I used a solid piece of oak for my "beater board" (forming block) that was one piece. I hammered nose, center, and aft ribs on the same form. Routing forms (cutting out parts), on the other hand, were separate.

For your router table, that'll be fine. That's how I did it before I invested in a lift plate. Works just fine if you can get it to plunge far enough.

For the router bit offset, you can use a bearing that is some degree smaller than the trim bit. Say you have a 1/2" trim bit like I used, put a 3/8" bearing on it, set your depth so the bearing rides on the template and the blade hits the target (but not the template), and you get a 1/16" offset on your cut part.

[Chris In Milwaukee]

Good catch

[JimParker256]

Chris, you can edit your post to change it to 1/4" so that someone using Tapatalk (which apparently doesn't show "comments") won't be misled... Just click "edit" right below your post.

[Chris In Milwaukee]

All fixed :-)

[Texaspilot]

Thanks Chris. Great advice.