Cutting a T-slot in thick aluminum?

[scottcox]

Hi Folks.

I just called Shopbot to purchase a full length (12ft) aluminum t-track for my indexer. When I bought the alpha in April, they quoted me $400. Last Monday, I called and spoke to Martha, then Dianne, who transfered me to Sales. Well, she transfered me to Scott's voicemail.

I left a message with Scott explaining that I would like to proceed with the purchase. Two days later, hearing nothing, I called again and got him on the phone. He told me they had misquoted me earlier and they didn't sell those. I'm on my own.

So......

I just bought a 12ft length of 1.25in x 6in aluminum bar (6061). I need to mill a t-slot in it, full length, with my alpha 5x10. I'm comfortable with the speeds, feeds and the need for cooling the bit.

I could use some recommendations for bit suppliers, chip extraction/control and jigging to cut the full 12ft length on my 10ft machine.

Any help?

Here's the profile......


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[Brady Watson]

Scott,
Use a .500 end mill made for cutting AL (high helix) with 1" length of cut to do the .75" slot 0.9" deep. Then use a T-slot cutter such as MCMaster-Carr's #8789A16 with 1/2" shank & .5625" cutter diameter to do the slot in multiple passes. The 1st pass is going to take out quite a bit of AL, so you will have to go pretty slow and throw LOTS of air at it to evacuate heat & trapped chips. I would start cutting the T at .2 IPS & 13,000 and nudge it up or down in move speed as you go. Do NOT press the S-key during the cut or it will be a sad day. Be sure to wear decent eye protection.

-B

[scottcox]

Thanks Brady. This is the type of advice I need.

What I'm NOT finding is a t-slot cutter with a 1/2" shank that will give me the 0.2" undercut. From what I see there's not an option to adapt a Colombo 5HP to 3/4" collet, correct?

Also thanks for the warning on the s key. That would indeed be a sad day.

[Brady Watson]

See the 1st and 2nd ones with 1/2" shanks. The Colombo 5HP uses the ER-25 collet system which restricts you to a max of .625" shanked tools. I would use the one of the smaller cutters and just program it to do multiple Z heights to get you where you need to be. The @ 1/4" neck size and 9/16" cutter size should allow you to cut the slot size you are looking for without a problem. Since you will have the 3/4" wide portion milled out, you have approximately +0.25" you can go above the slot centerline and -0.25" below it. If I were doing it, I would start the cut about 1.5" before and after the AL extents using multiple parallel machine along vector toolpaths. Think outside the box here...nowhere does it say that you have to run this mill down the Y centerline of the AL to get your finished size...In fact, it is better that you do one centerline pass, then one up in Y and one down in Y to keep cutter loads down. Set your safe Z way up to be sure to clear the whole deal, or just keep your wits about you when cutting.

It's late check my math...the 2nd cutter in the list might be the right choice.



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-B

PS- I'm sure we would all like to see pics of your success when you have it done!

[Brady Watson]

OK...here's the problem, using your measurements, you are not going to be able to do it. I went out to the shop and measured the T-slot AL pieces that came with my Alpha indexer (appear to be same spec as my PRT indexer plates) Dimensions are as follows:

Bolt shank slot is .5625" wide, not .75" wide
T-slot under cut max width is 1.00" wide, not 1.15" wide
T-Slot depth from bottom of slot to undercut is .375" not .45"

No sense in reinventing the wheel...If you are using a SB indexer then you really do NOT want the extra clearances that you have allowed for. As it is, the current dimensions have some clearance to them and mounting the indexer to the X rails as some will tell you, there is plenty of axial play in the slot to misalign the headstock & the tailstock centers.

Looks like I spoke too soon...you are right...you need a 3/4" collet to handle the t-slot mill to get you to 1.000" at the bottom. Know anybody with a Bridgeport?

Just as an idea...what about buying T-slot like Rockler sells and inserting it into the AL stock that you have? This way you just have to mill out a pocket or slot for the extruded t-slot to slip into and then screw it and/or epoxy it into place.

-B

[gerald_d]

Scott, I would rough out most of that slot on a tablesaw saw first (dado). Also, Do you have to copy the T-slot of the original rail exactly? You might be able to use angled dovetail cutters (or angled tablesaw blade) if you adapt the item that sits inside the rail.

[waynelocke]

Why not use a wood such as hard maple. Cut a groove of the needed size and then bolt or screw on 2 aluminum or steel, plates to form the T Slot. Or use Aluminum instead of the wood. Mill a slot and then bolt on the top plate.
Wayne

[gerald_d]

Wayne, Scott has already bought the solid alu.

[myxpykalix]

Hey scott...I know you already have the aluminum but you might try looking here:
http://www.8020.net/
They have extruded aluminum T track in different configs that might work for you. Its not that cheap stuff you get from rockler, My legacy ornamental mill is made from this stuff.

[scottcox]

Keep 'em coming guys. These are great ideas and I'm open to anything that solves my problem.

So far we have....

1- Find the right t-slot cutter for my collet size
2- Place an store-bought t-slot insert into a groove
3- Create my own with a wood base and steel plates



Brady, The profile that I posted is exactly what I have right now (but I have just two short 2ft sections). When I bought the 12" 25/1 ratio indexer in April, they said they had just beefed up the base from the previous setup. That's probably where you see the difference.


The 12ft section of 1.25 x 6 inch 6061 cost me about $335 US after tax. I could eat that cost and use the aluminum for something else, but honestly I'll like to be able to mill it myself.

Or am I a glutton for punishment? :-)

[Brady Watson]

So far I like the 8020 suggestion the best...Don't know why I didn't think of it earlier. Seems like a perfect solution - Thanks Jack


-B

[scottcox]

Gerald,

The bottom of the indexer base and tailstock have tabs for the size indicated and I already have the bolts that have the rectangular head, so I just went that direction. If I can't find the appropriate cutter, I may have to look at alternatives like that. Thanks.

[oddcoach]

Like Brady says think outside the box. Take your piece of aluminum rip it in half lengthwise. You can then mill 1/2 a slot in each half with it up on edge. Then on the bottom mill out some places for some 1/4 inch plates to be able to put the 2 halves back together, or you could just bolt the 2 halves to the table individually
John

[scottcox]

Jack, That looks like a great idea, but they don't show a slot profile that meets the needs. Did I miss it?

BTW: I believe the tailstock base tabs are cast so I don't have to much leeway on changing the slot shape.

Good thinking John. That's another very effective option.

[Brady Watson]

A piece of 3 or 4" steel C-channel and 2 strips of 2 X .25" steel bar can be welded up to make a t-track too...Wayne isn't this what you did on yours?

-B

[myxpykalix]

Just for grins i took out the extra track i have for my legacy and took a couple pics. Here is what i found. I didn't think of this till i closed the shop but if you look at "rail1.jpg" I didn't measure the slot opening however if you look at your retaining bolt measure the piece that goes in the slot. The slot on this particular design needs to be at least 1/4" smaller. I could wiggle the bolt and it would come up thru. I could get the specific demensions if you need them. Also you would need some side support (a couple 2x4's?)for lateral support. I bought that at a highly inflated price from legacy at $1.00/inch, that 5 ft piece cost $60.00 im sure you can find it cheaper. hope this posts ok. If you need more pics or info email me

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[gerald_d]

A bit of thread drift... I see quite a few people have "notched" their tables like in the pictures above. With a huge gusset in each frame to the left of the notch, but no gussets inside the notch. Three smaller gussets will be stiffer than the single big gusset.

[scottcox]

Update:

I've just ordered a roughing bit (65-026 Super O Upcut - $53) from Onsrud to cut the 0.9" deep, 3/4" wide groove and Whitney Tools is taking their T-slot cutter (805000M42) which comes with a 3/4" shank and cutting the shank down to 1/2" to fit my spindle (new Whitney part # 805000M42SH1/2) . That cost about $120.

The aluminum bar is in the shop waiting for the bits so in a week or so I should have a success story... or lots of questions!

Gerald: I was surprised at the level of deflection when weight is added to the table. I would beef it up quite a bit or use rectagular tubing with gussetts next time.

[gerald_d]

IMHO, the angle iron used under ShopBotter's tables is far too light, and that is probably where most of the resurfacing/flatness woes come from. When you notch those flimsy angle irons for an indexer, you are really inviting problems.

[beacon14]

The newest model shown at the IWF had much beefier cross braces

[gerald_d]

That must be the "E Table (http://www.shopbottools.com/files/manual/E%20Table%20assembly.pdf)" where the cross supports are made of corrugated sheet. Those cross-supports will be stiffer, but they will block a lot of access to the underside of the support board because they are quite wide? Makes for easy/light shipping by SB, but the DIY'er will be better off with standard C-channel.

[scottcox]

!! Update !!

Kids, don't try this at home. Shopbotters, go right ahead !

So I was a glutton for punishment and decided to mill my aluminum T-track on my shopbot. Cutting this much aluminum was very slow, so I had to put it aside several times for "cash-now" jobs.

I finally finished the milling, I've got the indexer trough struts drilled and it's ready to shim and mount.

Here's a couple of pictures......


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[Brady Watson]

Nice job Scott! See...you really can 'mill' AL on a Bot


-B

[scottcox]

Another Update.....

Some pictures of the indexer T-track installed. I shimmed between the track and each rib with a reference to my bit, so this thing is straight and level within a couple of thousands the full length.So now I can slide out for 10+ ft columns or down to an inch if I choose.

Does this count as "extreme shopbotting", Brady? :-)


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Here's a picture of a 32 inch "bar element" done in the round into eastern red cedar. The pictures don't do it justice. It looks much better in your hands.


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[conceptmachine]

nice work scott!!!
---shawn

[paco]

Whoohoo! Nice work Scott!

I like the lizard column project. How long to machine? How big it is?

...was wondering; did the slot cutter survived (still in shape)?

Did you built the indexer because projects are already sold? If not yet, do you believe you'll sell enough/much of turning projects?

[scottcox]

Thanks Shawn.

I knew I was destined for fun with the indexer the moment I saw it.

[myxpykalix]

Is that the "aromatic" cedar? Give us some details, how tall, how long to cut, how did you design the file, ect...inquiring minds want to know!

[scottcox]

Fast fingered Paco: Thanks. The lizard took about 3 hours total. 1 hour to rough (from a 6x8 inch blank) and 2 hours to finish. And the t-slot cutter DID survive. I was gentle with it becasue I didn't want it to break before I finished the t-track. And I've already got another job lined up for it. Something totally different but needing the exact shape (to hold a roller bearing). And the indexer will definitely pay for itself if I can find the time to use it.

Jack: This is eastern red cedar. I don't know if this is considered the same as aromatic, but it DOES have a distinct aroma to it. The lizard project is 32" tall with a 4inch center post remaining from a 6 inch blank. Took about 3 hours to cut. See my other post about the methods. (I don't know how to link to it.)