# A little advice needed on miter joints



## tjb (Oct 4, 2017)

Hello, All.

I wonder if any experts out there could possibly give me some advice on how to improve on producing mitered joints in aluminum.  Attached are some pix of a small tray that I made - mainly for practice on how to machine miter joints.  Note:  This project turned out far nicer than I anticipated for a 'practice' piece, but the finish is less than pristine.  At this point, the plan is to either paint it or have it powder coated to cover up the machining marks.

Here's a picture of the finished product:



It's a rather simple tray, but my challenge and purpose was figuring out how to make sturdy mitered joints that will not easily come apart.  (The next project will likely be a little more substantive.)  Before beginning the project, I decided that each joint would be stable if I had pins going into it from each face of the 90 degree angles.  Because of the relatively small size, I ended up putting two on one face of the angle and one on the other.  Here are some photos (note that the pins are off-center to allow for the bottom plate):






Calling these 'pins' is a bit of misnomer.  It occurred to me that the most secure hold would be to drill, tap, and use screws - then cut off the heads.  So they look like pressed pins, but they're actually screws.
Now on to my question:
I proceeded as follows (In retrospect, it occurs to me I should have taken pictures.  Sorry):
1.  I cut the sides to length and then mitered with a 45 degree end mill, making sure that the opposite pairs were exactly the same length.
2.  I independently joined a long- and short- pair together as follows:
   a.  I bolted a 90 degree angle plate to a 2-4-6 block,
   b.  mounted that in the chuck on my mill,
   c.  securely mounted each piece to the angle plate,
   d.  then drilled, tapped and screwed the pieces together.
3.  I did this for both pairs of long- and short- sides, resulting in two 'L;shaped' pieces.
4.  I then rough-assembled the two pairs I made (along with the bottom), and used a 1-2-3 block and clamps to tightly secure one of the unconnected joints.  I set this up in my mill chuck, and drilled/tapped/screwed.
5.  Changing the 1-2-3 block to the diagonal corner, I repeated step 4, resulting in all four sides being secure and square.
6.  All holes were drilled and tapped to 3/4", and I used 1" 10-32 machine screws.  Throughout the process, I cut off the heads of the screws and ground them flat with a bench sander.
7.  Did some final sanding to prepare it for painting.

Here's the question:  The final 90 joints are VERY secure, but the method was extremely tedious.  I found that regardless of how well I clamped them, when the drill bit AND the tap transitioned from the horizontal piece to the vertical piece along the 45 degree joint, it wanted to 'walk'.  With much effort, I got the job done, but I wonder: Is there a better way to make these kinds of joints?  I suspect I'll need to do several more, and if anyone has a tip on set-up or proper jigs to use, I'd love to hear it.

Regards,
Terry


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## neshkoro (Oct 4, 2017)

You might be better drilling a clearance hole in the top layer. The clearance hole will pull the parts together than trying to thread both parts. 


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## neshkoro (Oct 4, 2017)

I hit the send button too soon. Maybe a nice flat head screw might not look too bad. Might make it look like a professional job. That way you wouldn't have to worry about the parts moving around while you are drilling and tapping. 


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## francist (Oct 4, 2017)

Wow, good on you for sticking with that and coming up with a pretty nice looking job! 

In the woodworking world -- and your choice of joint here is really more a woodworking type of construction -- one of the ways around that full-mitre corner is one that is crossed with a rabbet joint. Best of both worlds in that it gives a mitred appearance to the corner (ie: no visible lap), but the rabbet faces allow for a 90-degree attack and purchase for pegs or dowel joint. Less likely to walk on the mitre face that way, plus if using a screw fastener as you are the screw pulls at a straight-on attack rather than obliquely which can have a tendancy to slide.


-frank


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## RJSakowski (Oct 4, 2017)

If you are looking for a decorative  and aesthetically pleasing corner joint, you might want to consider using a dovetail.  Properly made, the dovetail will be self locking if a single pin from the bottom is used to lock the tails.


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## rwm (Oct 4, 2017)

Would you consider welding the joints on the inside?
Robert


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## kd4gij (Oct 4, 2017)

I always use *18-8 Stainless Steel Hex Drive Flat Head Screws  for that type parts.*
*https://www.mcmaster.com/#standard-flat-head-screws/=19o7tzi





*


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## tjb (Oct 4, 2017)

neshkoro said:


> I hit the send button too soon. Maybe a nice flat head screw might not look too bad. Might make it look like a professional job. That way you wouldn't have to worry about the parts moving around while you are drilling and tapping.
> 
> 
> Sent from my iPhone using Tapatalk


Yes, I thought about that approach, but my objective was to have flat sides.  Obviously, a clearance hole would not allow that.  I think your idea would work fine if weren't for that little detail.

Thanks for responding.

Regards


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## tjb (Oct 4, 2017)

francist said:


> Wow, good on you for sticking with that and coming up with a pretty nice looking job!
> 
> In the woodworking world -- and your choice of joint here is really more a woodworking type of construction -- one of the ways around that full-mitre corner is one that is crossed with a rabbet joint. Best of both worlds in that it gives a mitred appearance to the corner (ie: no visible lap), but the rabbet faces allow for a 90-degree attack and purchase for pegs or dowel joint. Less likely to walk on the mitre face that way, plus if using a screw fastener as you are the screw pulls at a straight-on attack rather than obliquely which can have a tendancy to slide.
> 
> ...


Thanks, Frank.

In fact, my objective was to copy a woodworking miter onto aluminum.  (The project I have planned will have exposed ends, so I want the miter to be visible.)  I think your suggestion of a combination miter/rabbet joint is an improvement.  And it should be aesthetically appealing as well.  Thanks for the suggestion.

Regards,
Terry


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## tjb (Oct 4, 2017)

RJSakowski said:


> If you are looking for a decorative  and aesthetically pleasing corner joint, you might want to consider using a dovetail.  Properly made, the dovetail will be self locking if a single pin from the bottom is used to lock the tails.


Thanks, RJ.

Never tried doing dovetails before, but I agree: they are a beautiful thing to behold.  Any tutorials you can point me to?

Regards,
Terry


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## tjb (Oct 4, 2017)

rwm said:


> Would you consider welding the joints on the inside?
> Robert


Thanks, Robert.

Yes, life would be much simpler with a weld, but my application requires a clean, crisp inside corner.

Thanks anyway.

Regards,
Terry


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## tjb (Oct 4, 2017)

kd4gij said:


> I always use *18-8 Stainless Steel Hex Drive Flat Head Screws  for that type parts.*
> *https://www.mcmaster.com/#standard-flat-head-screws/=19o7tzi
> 
> 
> ...


I thought about using a countersinking screw, but I need the outside surface to be flat, flat, flat.  Maybe I'm underestimating myself, but I was concerned that over- or under-cutting the countersink might result in a very ugly mismatch.  Do you run into that issue?

Regards,
Terry


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## neshkoro (Oct 4, 2017)

Set the depth stop on the drill press and they will look very professional! Make the head just slightly under the surface. 


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## RJSakowski (Oct 4, 2017)

tjb said:


> I thought about using a countersinking screw, but I need the outside surface to be flat, flat, flat.  Maybe I'm underestimating myself, but I was concerned that over- or under-cutting the countersink might result in a very ugly mismatch.  Do you run into that issue?
> 
> Regards,
> Terry


Because flat head screws have a short cylindrical section, there would be a small groove on the circumference of the screw head if the screw was set flush.  There would be two work-around's.  Use a countersink the same diameter as the screw head or very slightly larger or set the screw proud and machine them flush after the box was assembled. Another technique would be to use a low profile socket head cap screw and set it below the surface and follow with a plug.  With finishing, the plug would virtually disappear into the wall of the box. 

It may be sufficient to use aluminum rivets.  Two cross drilled holes  from each side should prevent the joint from opening.  A swab of LocTite inserted into the hole before driving the rivet will help to hold it tight.  make a small scratch on the side of the rivet to permit any trapped gas or liquid to escape.  After seating the rivet, machine it flush and finish for a virtually invisible fastener.

When I was making aluminum cases for custom electronic enclosures, I would, on rare occasion, put a hole in the wrong place.  To repair the hole, I would countersink from both sides and make a short aluminum plug.  I carefully peened over on both sides and finished flush. then I wire brushed with a fine wire wheel which resulted in an invisible repair.  It was a bunch of work and enough of an annoyance that I was more careful not to repeat the error but it saved a case that I had considerable time invested in.


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## crazypj (Oct 4, 2017)

If you were making them from two different metals (eg, brass and aluminium) woodworking 'box joints or dovetails would look the nicest. As it is, if properly finished, you wouldn't see much of any joint so you 'need' the different light reflection from machining marks A small dovetail cutter ain't very expensive but mounting bars upright may be a clearance issue? There are plenty of tutorials for woodwork dovetails, some VERY EXPENSIVE wood planes are made with steel, brass or bronze dovetail plate bodies (or combinations of same) Even a Norris' style kit isn't cheap
http://www.ebay.com.au/itm/Norris-type-steel-dovetail-17-jack-plane-kit-/172856457356


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## Asm109 (Oct 4, 2017)

Two ways to stop the drill from walking sideways.

1. Use a 2 flute endmill smaller than the tap drill size.  Plunge down until you have a full diameter flat landing spot in the lower piece. Tap drill and tap.
2. Make a drill bushing guide plate that you clamp on top to guide the drill.

Drill bushings are hardened steel cylinders that guide the drill so it cannot walk.


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## tq60 (Oct 4, 2017)

Try this with scrap...

Build a fixture to hold parts and that is easy...Place angle iron on flat plate with bolts or welds then with end mill make true and cut both x and y at same setup so mill table accuracy is transferred to fixture.

Make another fixture for holding at 45 degree angle.

Both fixtures hold material with standing on small side and lengthwise along the table.

Last fixture is a chunk of metal that fits over the end or corner and has holes pre drilled as guides.

Next make all lengths correct and square.

Using top fixture place parts in but the corners are clamped tight in butt joints.

Place the last fixture over the end on the outside part and drill holes through the outside of that part then into the end of other part.

Witness mark both parts.

Now swap orientation of parts and drill opposite holes.

Now tricky part.

Mount 45 degree fixture and cut the miter with standard end mill.

If you can get all done well and the miter are not over cut the predrilled holes now will line up and miter perfect.

You also could just use the drill guide with the first fixture to hold the fully machined parts then drill the holes.

Given you are grinding off screws and powder coating then the pins can be anything that can be soldered so you could solder instead of screws.

Last option is taper pins which would require modifying the reamer for shorter length or drill deeper holes or both.

Then smacking the taper pin in would be a tight fit without any gaps.

A drop of lock tight insures no movement.

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## kd4gij (Oct 5, 2017)

I just set the stop on the mill or drill press to set them flush. And use stainless as the look nice.
If you don't have a good stop on your drill press, you can make one of these for an 82dg center drill.
https://www.harborfreight.com/7-piece-drill-stop-set-38336.html


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## crazypj (Oct 5, 2017)

Aluminium has a particular affinity for stainless steel and will corrode over time. For a tray it may not be a problem but making over-length aluminium pins then shrink or force fitting them (plus cut and polish after fitting) would give a just about invisible joint. It will probably be a lot more work making pins but could easily end up with a 'How did he do that?' piece


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## kd4gij (Oct 5, 2017)

I have never had an issue except in salt water. If the application is near water, I use anti seize.


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## crazypj (Oct 5, 2017)

It's an issue when you have parts heating and cooling (motorcycle engine covers).
Last several years I've used plumbers Teflon paste, works better than anti-seize if your not going over 400f. Apparently, copper based anti-seize helps galvanic corrosion with stainless steel screws in cast aluminium engine blocks. The high temp nickel based stuff is about the same IIRC? As I 'play' with 40+ yr old 'imports' I would like to think I'm helping keep them around at least another 40~50 yrs


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## woodchucker (Oct 5, 2017)

tjb said:


> Yes, I thought about that approach, but my objective was to have flat sides.  Obviously, a clearance hole would not allow that.  I think your idea would work fine if weren't for that little detail.
> 
> Thanks for responding.
> 
> Regards


you can still have a clearance hole  , a clearance hole allows the screw to go through with out rubbing Your countersink would still prevent the screw from lowering into the side.  

Looks well made, as a woodworker that joint was very familiar to me. Would never have thought to use that for metal working. But  it sure do look purty.


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## tjb (Oct 6, 2017)

neshkoro said:


> Set the depth stop on the drill press and they will look very professional! Make the head just slightly under the surface.
> 
> 
> Sent from my iPhone using Tapatalk


Thanks.


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## tjb (Oct 6, 2017)

RJSakowski said:


> Because flat head screws have a short cylindrical section, there would be a small groove on the circumference of the screw head if the screw was set flush.  There would be two work-around's.  Use a countersink the same diameter as the screw head or very slightly larger or set the screw proud and machine them flush after the box was assembled. Another technique would be to use a low profile socket head cap screw and set it below the surface and follow with a plug.  With finishing, the plug would virtually disappear into the wall of the box.
> 
> It may be sufficient to use aluminum rivets.  Two cross drilled holes  from each side should prevent the joint from opening.  A swab of LocTite inserted into the hole before driving the rivet will help to hold it tight.  make a small scratch on the side of the rivet to permit any trapped gas or liquid to escape.  After seating the rivet, machine it flush and finish for a virtually invisible fastener.
> 
> When I was making aluminum cases for custom electronic enclosures, I would, on rare occasion, put a hole in the wrong place.  To repair the hole, I would countersink from both sides and make a short aluminum plug.  I carefully peened over on both sides and finished flush. then I wire brushed with a fine wire wheel which resulted in an invisible repair.  It was a bunch of work and enough of an annoyance that I was more careful not to repeat the error but it saved a case that I had considerable time invested in.


Thanks, RJ.
Those are good suggestions, but for this immediate application, any sort of countersink approach or cap screw won't work.  Using 3/8" stock and a miter joint doesn't leave much room for the countersink or a plug.  My approach is essentially identical to your other suggestion of setting the screw proud and then machining flat.  Only difference is I milled and tapped the hole to 3/4" and used a 1" screw, thereby machining off the screw head plus a little bit of thread.  That made for a very secure joint with a nice appearance.

I like your idea of using rivets.  Never thought of that and, since the finished joint will not be subjected to a lot of torque or pressure, that may be sufficient.  I'll look into it.

Thanks again for responding and the thoughtful suggestions.

Regards


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## tjb (Oct 6, 2017)

crazypj said:


> If you were making them from two different metals (eg, brass and aluminium) woodworking 'box joints or dovetails would look the nicest. As it is, if properly finished, you wouldn't see much of any joint so you 'need' the different light reflection from machining marks A small dovetail cutter ain't very expensive but mounting bars upright may be a clearance issue? There are plenty of tutorials for woodwork dovetails, some VERY EXPENSIVE wood planes are made with steel, brass or bronze dovetail plate bodies (or combinations of same) Even a Norris' style kit isn't cheap
> http://www.ebay.com.au/itm/Norris-type-steel-dovetail-17-jack-plane-kit-/172856457356


No doubt about it: those joints would be beautiful with two different metals.  Such an application is something I considered.  One thought I had was to make the sides out of aluminum and the pegs/screws out of brass.  That would look pretty nice - assuming, of course, the finished product is not painted.

Thanks for responding.

Regards


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## tjb (Oct 6, 2017)

Asm109 said:


> Two ways to stop the drill from walking sideways.
> 
> 1. Use a 2 flute endmill smaller than the tap drill size.  Plunge down until you have a full diameter flat landing spot in the lower piece. Tap drill and tap.
> 2. Make a drill bushing guide plate that you clamp on top to guide the drill.
> ...


Good suggestions.

#1 sounds like a good strategy.  The drill bit is not actually what 'walked'.  The bigger issue was the vertical section of the miter joint wanted to wobble slightly as the drill bit transitioned into it from the horizontal piece.  It took some serious clamping effort to keep that from occurring.  I suspect using an end mill first would minimize or totally eliminate that problem.

Thanks again for responding.

Regards


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## tjb (Oct 6, 2017)

tq60 said:


> Try this with scrap...
> 
> Build a fixture to hold parts and that is easy...Place angle iron on flat plate with bolts or welds then with end mill make true and cut both x and y at same setup so mill table accuracy is transferred to fixture.
> 
> ...


Wow!  That's a very thoughtful suggestion.  I had to read it several times to visualize it, but I think I've got it.  (Do you have such a setup?  Any pix?)  I see what you mean about milling the miter being the 'tricky part'.  That step would definitely require a lot of precision.

Thanks for the suggestion.  Making the fixture would be a challenging and fulfilling exercise in itself.

Regards.


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## tjb (Oct 6, 2017)

kd4gij said:


> I just set the stop on the mill or drill press to set them flush. And use stainless as the look nice.
> If you don't have a good stop on your drill press, you can make one of these for an 82dg center drill.
> https://www.harborfreight.com/7-piece-drill-stop-set-38336.html


Thanks for the link.

Regards


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## tjb (Oct 6, 2017)

crazypj said:


> Aluminium has a particular affinity for stainless steel and will corrode over time. For a tray it may not be a problem but making over-length aluminium pins then shrink or force fitting them (plus cut and polish after fitting) would give a just about invisible joint. It will probably be a lot more work making pins but could easily end up with a 'How did he do that?' piece


Good suggestion.  And I LOVE 'How did he do that?' responses!
Regards


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## tjb (Oct 6, 2017)

woodchucker said:


> you can still have a clearance hole  , a clearance hole allows the screw to go through with out rubbing Your countersink would still prevent the screw from lowering into the side.
> 
> Looks well made, as a woodworker that joint was very familiar to me. Would never have thought to use that for metal working. But  it sure do look purty.


Thanks for responding, Woodchucker.  Countersinking on this particular application simply won't work because I'm only using 3/8" flat stock.  That doesn't allow much room for a countersink on a miter joint.  That's a good suggestion if I perform a similar exercise on thicker pieces.

Thanks for the compliment.  You can't imagine how meaningful it is.  My objective was actually to replicate a woodworking-style miter joint in aluminum.  It's encouraging to receive a compliment from a real woodworker.  Thanks!

Regards.


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## DaveInMi (Oct 6, 2017)

tjb said:


> No doubt about it: those joints would be beautiful with two different metals.  Such an application is something I considered.  One thought I had was to make the sides out of aluminum and the pegs/screws out of brass.  That would look pretty nice - assuming, of course, the finished product is not painted.
> 
> Thanks for responding.
> 
> Regards


Box or finger joint would be especially appealing to my eye with alluminum and brass.  Set up would be much simpler than a dovetail and I like the look better.


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## neshkoro (Oct 6, 2017)

I think you are making it more difficult than it should be. If you align the corner assembly ( clamp a block into the corner of the joint) and then drill it as an assembly (drill, counter drill, countersink and tap) it should work perfect. 


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## whitmore (Oct 6, 2017)

tjb said:


> I wonder if any experts out there could possibly give me some advice on how to improve on producing mitered joints in aluminum.


Well, would an invisible joint help?  If you put a couple of keyholes into the beveled edges, and machined
dumbbell shaped fasteners, it could take a dab of epoxy to lubricate, and slide into position.   Once the
epoxy hardens, no more sliding.
<https://www.aliexpress.com/item/New...-Bits-Trimming-Knife-1-4-x-9/32800487214.html>


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## tq60 (Oct 6, 2017)

tjb said:


> Wow!  That's a very thoughtful suggestion.  I had to read it several times to visualize it, but I think I've got it.  (Do you have such a setup?  Any pix?)  I see what you mean about milling the miter being the 'tricky part'.  That step would definitely require a lot of precision.
> 
> Thanks for the suggestion.  Making the fixture would be a challenging and fulfilling exercise in itself.
> 
> Regards.


No photo but Google art frames and fir woodworking there are many options as samples

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## tq60 (Oct 6, 2017)

tjb said:


> Wow!  That's a very thoughtful suggestion.  I had to read it several times to visualize it, but I think I've got it.  (Do you have such a setup?  Any pix?)  I see what you mean about milling the miter being the 'tricky part'.  That step would definitely require a lot of precision.
> 
> Thanks for the suggestion.  Making the fixture would be a challenging and fulfilling exercise in itself.
> 
> Regards.


We do have a drill guide or 2 that we have made for various projects.

One was steel and other aluminum.

We needed a square to surface hole at a repeatable place reference to a corner so we took flat aluminum and milled it out so it could rest on the surface with a recessed area causing 2 faces for stops 

We then dug in the bolts and since we had many 5/8 grade 2 leftover from shop we drilled and tapped 5/8 on the plate where the hole needed to be and in the lathe drilled the 1/4 hole in the bolt and then screwed it into the plate and held with jamb nut.

Easy to make and length of bolt insures hole is drilled straight with portable drill so clamping your project can be done flat 

If you offset the hole then flipping fixture allows it to be used on 2 sides
.

Have one  side be centered and other side as the offset one 

It then can be used first to drill holes then before moving tap them as it holds tap straight too.

Then use Allen set screws to temporary hold in place then flip and do last &olé on other side needing 2.

Insert final screws then do next corner.

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## Silverbullet (Oct 8, 2017)

There's a way to cut a lengthwise dove tail that pulls the joint tight and locks it in place . I use to use in drawers I built in wood. I think it would work in metal it's a little bit like a gib on a machine slide.


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