First, I will post pictures, design, etc...when I have a little more of it built. But right now I have the following problem:

Explanation of Problem:
I have my T-slots cut, and have the hardware to put it together. I use brackets in some places (a no-brainer) and Anchor-Fastner/Butt-Fastner (http://home.comcast.net/~kr4495/cnc/hardware/Hardware.html) in others. The Anchor-Fastner/Butt-Fastners are round disks that sit in the T-Slots, but you have to drill a hole somehow for them to sit in the metal extrusions. The hole has to be 13/16 diameter with a flat bottom, about 3/4" deep. T-slots Inc does sell a bit which they call a "13/16 Counterbore Cutter". They don't say wheather it's for a drill or a mill. It costs $62.50 US which just isn't going to happen. I need a cheaper fix.

Question:
So, how can I drill a 13/16" diameter hole, 3/4" deep, with a flat bottom in aluminum with my Ryobi 10" Drill Press?

Things I thought of:
1. I thought about using a regular bit and just not going all the way down, then taking my air-powered die-grinder and boring the hole deeper. Very messy and not very precise.
2. Thought about using a Pilot-Point bit which is flat with a small guide point in the middle. But the guide point would put a 1/4" hole all the way through the metal. I don't like that.
3. I can't afford to take it to a shop.

Any ideas? Some special or weird bit? What am I overlooking?

Drill the hole to the depth needed with a normal drill. Then grind another drill of the same size, flat, use this to make the bottom flat. You might want to start with a smaller pilot hole first.

Gary :D

Start your hole with a 13/16" first to depth as you have mentioned, then take your drill bit to
the grindingwheel and grind the tip off by turning [spinning]
Then with the side of the grinding wheel, you can gash the face [chip rake] to center, or one
cuttingede slightly longer then the other, so it will for sure cut thru the center.
Then grind the relief angle, about 5 to 8 degree.
You can also make you drill point more blunt, instead of 118 degr., something like 150 degr. so
the diameter of 13/16 will go deeper, what makes it better for the flat bottom drill, it gives you more guiding length!
Konrad

What about a Straight Plunge, router bit (http://www.internationaltool.com/amanastraightplunge.htm) ? It is made for a wood router, but the shaft will fit my drill press. I think they are made for cutting wood but perhaps I can find a heavy-duty one. At $15-$20 the price is right. Do you think it is worth a try?

http://www.internationaltool.com/amanastraightplunge.htm
http://dwp.bigplanet.com/woodwork/pages/store/skudetail.nhtml?profile=displayroom&uid=11252&catuid=10226&returnURL=http%3A//dwp.bigplanet.com/woodwork/displayroom/category.nhtml%3Fcatuid%3D10226

I think you need to spin it much faster than a drill press can. A better solution would be to drill the hole to the proper depth, and then use a wood template with a straight bit with a bearing on top to square up the bottom.

Gerry

I have used a Forstner bit in a drill press on aluminum before - wasn't what it was designed for and it will probably make the real machinists cringe, but it worked for me. It churns out tons of very thin, foil-like swarf that you have to clear regularly, and it goes really slow and things heat up fast. I kept a spray can of WD-40 handy and tried to keep it lubricated, and I had to pause several times to keep it from getting too hot.

I'll bet if you drilled the 13/16 hole with a regular drill to remove the bulk of the material, then finished with the Forstner to just flatten the bottom, it would cut out a lot of the work.

Found a 13/16" bit here for $5.99:

http://shop.woodcraft.com/Woodcraft/product_family.asp?family_id=774&Gift=false&GiftID=

I hate having to recommend this chinese stufff, but you want cheap so here it is; use your regular 13/16 drill bit to go as deep as you can with it, then without moving anything use a chinese end mill (with center cutter) and plunge it into the hole to clear up the angle the drill bit left. These cheap end mills are...cheap, and you can get em from ebay, msc etc.

I wouldn't grind a drill bit if you are not experienced with it, if done wrong it will chatter like mad and might even twist and brake in the hole.

0.02 cents:)

H3ndriX

I looked at end-mills but couldn't find a cheap one with a suitable shank size of 1/2".

I went physically to:
1. Northern Tools
2. Harbour Freight
3. Home Depot
and not one of them had a 13/16 drill-bit, or a 13/16 Forstner bit, or anything else.

I ended up buying about the same thing T-slots Inc had but for half the price (and twice the shipping). MSC Industrial Supply doesn't tell you how much shipping is till they ship it. But, by that time they already have your credit card number and the order is processed. I assume shipping is a fortune. What kind of company does that? I won't do business with them again because of that. It's just insane.
I really spent too much anyway, but it looks like a nice tool - $28.81 + probably $20 shipping ( http://www.mscdirect.com/IWCatProductPage.process?Merchant_Id=1&Section_Id=536&pcount=15&Product_Id=5566 )

I also bought a regular 13/16 drill-bit off of Ebay. It was $11 with shipping (Paid more for shipping and handling then the bit sold for).

So much for "Cheap"...In for a penny, in for a pound!

Be carefull when you drill those holes. It will be tough with a drill bit since it will want to grab in the sloit. I used my first cnc. You may want to try using a regular router with a 1/2" (or less) endmill and a plywood fixture/guide.

E

I found some t-tracks at: http://www.woodpeck.com/14ttrack.html#492
These are cheaper than others and can use a regular 1/4" hex bolt as fasteners. This should be stronger than using a router bit and making t-slots from wood. Have you considered using t-tracks instead? I just placed an order for my new router.

I wasn't suggesting t-slots from wood, but to use a wood template and a router to make the holes in the t-slot.

Eric

Interesting products, what caught my attention is the slides. Has anyone tried using this as a cheap slide for CNC.

Kin Fong

http://www.embeddedtronics.com/

Originally posted by georgebarr
I found some t-tracks at: http://www.woodpeck.com/14ttrack.html#492
These are cheaper than others and can use a regular 1/4" hex bolt as fasteners. This should be stronger than using a router bit and making t-slots from wood. Have you considered using t-tracks instead? I just placed an order for my new router.

Kfong - good question. it could be a cheaper alternative to www.igus.com stuff. Looks about

http://www.woodpeck.com/14ttrack.html#492
$18 for 2 48" aluminum extrusions.
$10 for 24" of nylon guide bearing..

Probably pretty sloppy though, id imagine loading the slides against each other could work.. Maybe.

In my oppinion, IGUSs cheaper N series linear slides have a bit of slop in them as well. In comparison, IGUS 27mm rail is:
$30.00 for 2 48" extrusions
$20.00 for 4 "Drylin" Slide Shuttles

twice as much. maybe 3 lengths of the cheaper stuff with 3 4" long slides would be ok... maybe the would bind? ideas on that?

Seems like there is no side to side slop or very little, there is a gap it appears much like how tnuts are used. This won't be too much of a concern if they are mounted on the side of the gantry for the x axis and the gantry itself holds them in. Would be interesting if it does work. would be cheap, using multiple slides would drive up costs but would increase bearing loads. Would seem a good alternative to the rollerblade bearing setups I keep seeing, and certainly good enough for the model airplane cnc crowd.

Kin Fong

http://www.embeddedtronics.com/


Originally posted by vacpress
Kfong - good question. it could be a cheaper alternative to www.igus.com stuff. Looks about

http://www.woodpeck.com/14ttrack.html#492
$18 for 2 48" aluminum extrusions.
$10 for 24" of nylon guide bearing..

Probably pretty sloppy though, id imagine loading the slides against each other could work.. Maybe.

In my oppinion, IGUSs cheaper N series linear slides have a bit of slop in them as well. In comparison, IGUS 27mm rail is:
$30.00 for 2 48" extrusions
$20.00 for 4 "Drylin" Slide Shuttles

twice as much. maybe 3 lengths of the cheaper stuff with 3 4" long slides would be ok... maybe the would bind? ideas on that?

Well, the tool I bought works. But I think a Forstner bit would work just as well. This Aircraft-Counterbore bit has a hole in the middle for a guide. After making the large bore hole you then have to drill-out the aluminum left by the hole in the bit. Which pretty much leaves a small hole in the bottom of your bore hole (anyone following that?).
So, why not just use a Forstner bit which results in the same thing. It is half the price and can be found at most hardware stores.

My biggest problem seems to be chatter when I'm drilling through that first slot (the T-slot). The sides want to vibrate. So tomorrow I will shove some wood in the slot to see if it doesn't make it more stable. Once the bit hits the flat bottom it gets as smooth as silk and cuts perfectly.

A 13/16 regular drill bit turned out to be a nightmare! It gouges the metal and likes to chatter way to much. It vibrated so bad it made the chuck fall off my drill-press. Yikes! Don't use a drill bit! Bad mojo!

So, for anyone reading this in the archives:
1. Use a Forstner bit. They're cheap.
2. Set your speed to about 1000 rpm on your drill- press (or there abouts).
3. Go very slow.
4. Spray some oil on the cut area. Makes it a smoother cut. But it's messy.
5. Use dowling or some kind of wood stuffed into the T-slot to keep it from vibrating. You might just use some t-nuts and bolts to form a bridge on either side of the cut and try to cut between them. I like the idea of wood better.
6. Be prepared for metal shavings everywhere!
7. Do some test cuts before ruining good parts. I'm still practicing.

Hope this helps somebody!