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Makin' long dovetail saddles the quick & dirty way

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#1 Jim Chung

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Posted 02 December 2013 - 04:12 PM

I often have to have an ultra long dovetail plate for my scopes to reach the balance point because I eschew tubes and rings for my scope designs. To have one custom made can be pricey.

Here's what I do. Buy a piece of aluminum from your local Metal Supermarket, I went today for a 3"x20"x0.5" piece and they had an offcut piece lying around for which they charged me $15 cash. I angled my table saw blade to 30 degrees and cut on the right hand side of the blade to end up with 60 degree bevels. To prevent kickback I screwed a piece of wood on the fence to trap the piece of aluminum and fed it with a long dowel. Kinda dangerous but short of the blade shattering I can't think of anymore precautions I could take. Oh and do it outside on your driveway and wear a hoodie since the amount of metal shavings is unbelievable. I'm lucky that it is December and I can still do ATM on my snow free driveway in Toronto.

Don't forget to sand and file down the razor sharp edges and corners.

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#2 Jim Chung

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Posted 02 December 2013 - 04:13 PM

Finished product ...

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#3 Noisykids

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Posted 02 December 2013 - 04:20 PM

i know it's possible to machine aluminum with woodworking tools, but, jeez, the idea of doing it scares the pants off me. if i were going to do that i think i'd be more comfortable using a carbide bit in a 1/2 router. or bring it to my friend bob's machine shop and beg him to do it on the sport b3.

#4 mark cowan

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Posted 02 December 2013 - 04:34 PM

Definitely better with a router and carbide bit, I've done a lot of aluminum work that way. Oil helps too.

But looks good!

Best,
Mark

#5 Geo31

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Posted 02 December 2013 - 04:44 PM

Kinda dangerous but short of the blade shattering I can't think of anymore precautions I could take.


More risk than I would undertake...

Many years ago when I first took up woodworking, I had a similar bench saw and ran a piece through the tiled blade. The cut-off jammed between the blade and the throat plate (which was on the other side on mine) and both the throat plate and two carbide teeth went zinging past my ear. Had I been standing directly behind the work I may not be alive today.

In your case, with a longer piece sliding through the saw, it's probably a bit safer than what I was working with, but my experience makes me look long and hard at any set-up that could jam and kick back.

I'd also say a router table would be a better solution. I applaud your craftiness however.

Oh, and lastly, please tell me you normally work with the guards in place....

#6 MKV

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Posted 02 December 2013 - 04:59 PM

I think this is really dangerous. I've been a woodworker for many, many years and even I would readily look for alternative ways to make my dovetail. One that comes to mind that is much, much safer is using a bandsaw with a carbide tipped blade, and lots of cutting oil. Tilt the table to 30 degrees. No possibiity of kickback. Just let the blade cut at its own speed and don't force it.

I would definitely not recommend using tablesaw for tis at all. It's playing with fire.

regards,
Mladen

#7 HunterofPhotons

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Posted 02 December 2013 - 05:04 PM

..... To prevent kickback I screwed a piece of wood on the fence to trap the piece of aluminum and fed it with a long dowel.....


Jim,
Lest someone copy this technique as the safest way to do this, let me offer two improvements.
One, ditch the piece of plywood next to the blade. That actually increases your chance of a kickback by trapping the cutoff between the blade and plywood. A much safer way to do this is to position a featherboard below the blade. This prevents kickback of the metal piece as it enters the blade. The offcut naturally falls away from the saw blade in this arrangement. It's good practice not to stand behind the blade anyway just to sure.
A fancy featherboard
If you make your featherboard longer you don't need the stuff that rides in the miter slot, you can just clamp it to the table saw top.
Secondly, your push stick can be made much safer. A good push stick allows one to push a piece through but also allows one to exert downward pressure to hold the piece tight to the table, something your dowel won't do. Here is a safer design.
I, too, agree with the other posters that this is a dangerous activity at best. I'd let a metal worker do this. The cost would be minimal.

dan k.

#8 Jim Chung

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Posted 02 December 2013 - 05:37 PM

I have to agree with the thoughtful responses. This is the second time I've done this and likely the last time. If you guys knew what I do for a living you would be horrified that I would risk so much. I guess I'm just a sucker for finding a new way of doing something.

#9 Pinbout

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Posted 02 December 2013 - 06:04 PM

the only thing I hate about cutting alum on a table saw is the blade getting the alum chips sticking on the carbide tips. I cut it on the table saw also, I use a triple tip blade.

#10 Noisykids

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Posted 02 December 2013 - 06:16 PM

just try making those surgeon's knots, deep in someone's abdomen, by feel, gloves slippery with human fat. ain't easy with only three fingers on one hand.

#11 Norm Meyer

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Posted 02 December 2013 - 06:49 PM

I cut most of my aluminum with my woodworking band saw. It's
a lot safer no kick back. If you have a bandsaw with a tilting table all the better. If the table doesn't tilt you
could make a jig of with the proper angle to hold the stock.
I usually spray the blade (blade running) with WD40 before I start the cut. When the shipyard was building ships with an aluminum deck house I saw the mechanics cutting up to 2"
AL plate using Skil saws. They put the blades in backwards
and cut the AL almost like they were cutting wood.

Regards Norm

#12 StarStuff1

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Posted 02 December 2013 - 07:01 PM

For a few years I have been making dovetails out of red oak and faily thick aluminum flat bar stock. Everything is glued and screwed together with decking screws. So far no failures. This scope weighs something like 18 or so pounds.

The wood is cut on a table saw but the aluminum is cut on a band saw. Relatively safe compared to cutting thick aluminum on a table saw. :scared:

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#13 piaras

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Posted 02 December 2013 - 08:38 PM

We cut Al with saws any time. Go to a metal supply shop, they might be using a cold saw, or metal band saw. Table saw blade with carbide teeth not an issue. Check the blade information for non ferrous usage. Naturally Eye/Hearing protection is required even more than when cutting wood. Should be used all times at table saw anyways.

#14 piaras

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Posted 02 December 2013 - 08:40 PM

By the way, nice write up in S & T on that folded refractor that you talked about this summer at Starfest!
Pierre

#15 roscoe

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Posted 02 December 2013 - 10:54 PM

I cut a bunch of aluminum last summer on my tablesaw, It is a 10", but after doing a bunch of research, changed the blade for a 32-tooth carbide 7-1/4" skilsaw blade, put in regular direction (not backwards) The thinner kerf and lower tip speed keep the blade and stock from overheating, and aside from the noise and shrapnel, cuts 1/4" aluminum as easy as maple. I used good earplugs and wore a full-face clear plastic face shield, and held on firmly.
R

#16 roscoe

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Posted 02 December 2013 - 11:18 PM

Also, I am a big believer in the use of 'sleds' on a table saw - sleds are wood boxes or trays with strips on the bottom that run in the slots on a saw table, so instead of moving a piece against the table, you secure the piece in the sled and move the whole thing. More to hold on to, much less chance of the workpiece spinning out of control.

#17 tim53

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Posted 03 December 2013 - 01:25 AM

I make my "dovetails" with 1/8" x 3/4" aluminum channel and a stick of 1 by (hardwood or poplar, whatever I have laying around).

Here's the one I mounted my 6" f/10.3 Kludgescope on. I drilled holes in the channel pieces to run binder-head screws into from both sides (staggered so the screws don't run into one another). Takes maybe a half hour to make one of these when you have it laid out on paper or in your head:

Posted Image

Closer view:

Posted Image

-Tim.

#18 Jim Chung

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Posted 03 December 2013 - 08:36 AM

Excellent responses, I learned a lot about how to make less dangerous dovetail saddles. Thanks Pierre, glad you enjoyed my talk at Starfest! I was going to say I was a concert pianist but I do perform surgery, just not in the abdomen.

#19 John Jarosz

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Posted 03 December 2013 - 09:02 AM

Check the blade information for non ferrous usage



Cutting thick billets of aluminum on a table saw is pretty much SOP in any machine shop but it is not for the faint of heart.

I posted thisd before but here it is again: There are different grades of carbide. One of the variables in the different grades is toughness (resistance to fracture). For woodworking the shock from the impact of the carbide hitting the wood is much lower than carbide impacting metal.. Blades that are specifically identified as 'for non-ferrous use' are made from grades of carbide that are tougher and can withstand the higher impact loads. The cheapo carbide blades from the homecenter that are always on sale don't 'cut it'. (Pun intended) :grin:

I suppose it all depends on what you are familiar with. I've never seen anyone use a router on aluminum and I can't imagine it working well but others apparently do it successfully. Whether it a saw or router, feed rates, cutter speeds and the use of lubricant are important. Follow published guidelines, don't do this stuff alone. You want to have someone nearby who can take you to a hospital if necessary.

#20 careysub

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Posted 03 December 2013 - 09:51 AM

...
I suppose it all depends on what you are familiar with. I've never seen anyone use a router on aluminum and I can't imagine it working well but others apparently do it successfully.
...


FWIW McMaster-Carr carries carbide router bits specifically for aluminum:
http://www.mcmaster....er-bits/=pnb9ib

Use a small diameter bit, and preferably a variable speed router to keep the cutting edge speed down.

I got one of these bits to try, and chose the smallest (1/8"), but haven't tried it yet. So far I have done all my aluminum shaping with a b@st@rd file and a disk or belt sander, which work very well. Cutting an accurate slope on the edge of a long bar would be difficult this way though.

I NEVER hand-feed anything on my router table, don't even own a feather board. I ALWAYS use a jig/sled of some sort, in fact I built a rail-mounted sliding router table so that I can bolt/screw down the piece holder to a stable platform. When the right project comes along I'll try routing the edge of a piece of aluminum, but expect to take multiple very shallow cuts. I don't want to find out what it takes to break the bit.

#21 Chuck Hards

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Posted 03 December 2013 - 10:43 AM

I've been cutting and routing aluminum & plastics with woodworking tools for 30 years without a mishap. This specifically was the gist of my S&T article in March of 99. The tube rings, bridge plates, and other detail parts of those scopes were done like this.
I hesitated to post those methods here because I had years of woodworking experience on shop tools before I ever cut a piece of aluminum on the table saw or took a router to it. I wouldn't advise someone to try it as their first experience with non-ferrous metal fabrication. Much good advice has been posted in this thread already, just be careful and if you are timid about using these tools at all, DON'T DO IT alone. Work with someone with experience until you get the processes down.

Always wear eye protection. With aluminum, I typically wear both safety glasses AND a full face shield.

#22 lukasik

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Posted 03 December 2013 - 10:52 AM

Ditto on the safety glasses and face-shield Chuck. I cut a lot of aluminum on my table saw. Make sure there is nothing whatsoever to distract you from the task such as hot chips down your shirt! Button up your collar. WD40 as a lubricant works OK but can smoke a bit. The waxy band saw lubricant can mitigate chip buildup on carbide tips.

Above all be safe. If you're really intimidated by the task, think again before proceeding. I also wouldn't tackle thick stuff before gaining experience on thinner material.


Best Regards,

Bob

#23 Geo31

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Posted 03 December 2013 - 11:46 AM

And once again (CANNOT be stated enough), use guards as much as possible. They are there to save your fingers and maybe even your life.

Don't ever work distracted or tired. Easiest way to remove fingers or worse.

I was on a speaker building mailing list some years ago and chatted with a fellow about his Delta Unisaw (I still really want one of those). He had wanted one for a long time as well. He got it all set up, sans guards, and just HAD to try it out, despite being tired. He described for me how he actually watched himself run 3 fingers through the blade of the saw.

Think twice. Think three times. Don't work distracted. Don't work tired. And DON'T take anything for granted when using power tools - especially when running aluminum.

#24 woodscavenger

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Posted 03 December 2013 - 11:53 AM

I like the aluminum channel/wood combo. Nice and clean

#25 Old Dinosaur

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Posted 03 December 2013 - 11:57 AM

I've cut a lot of aluminum plate on a table saw, including many dovetails. I use a fine carbide tipped blade.
Go slow, use care like you would with any power tool.






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