Turning a tapered column

[johnm]

Folks -

I've just set up our lathe similar to Wayne Locke's setup, sans the stepper...

Quick question on a time estimate - I need to run a taper on a column from 3" in diameter to 1" over 36". I've got a spindle and can use any cutter.

For those that've done this, I'm all ears - time estimate, bit & feed/speed suggestions, how not to tear up 1) the spindle, 2) the work and 3) Me...

TIA,

John

[robert_cheal]

I am all ears too, I am about to set something up and just not brave enough to try anything yet.

Robert

[Brady Watson]

Gents,
Go to: C:\Program Files\ShopBot\Virtual Tools\Indexer and read the "Indexer Virtual Tool Instructions.pdf" There are several good tutorials in the PDF. Addtionally, in SB3, go to Tools->Indexer and mess aroud with some of the different options you have. Bill Young did a great job (and Grant too) supplimenting the indexer documentation and created many utilities to make life easier.

If I wanted to create a tapered column, I would create an angled line in PW, Insignia or ArtCAM and use the Indexer utilities to make that profile into a rotary file. You'll get a good idea how to do this by reading the PDF.

As far as feeds and speeds go, you can get a good idea by using a block of insulation foam (white, pink, blue etc). You can glue up blocks using wood glue. Then, just start milling. If you make a mistake, you'll only be gouging foam...not wood. It's a great way to have your 'training wheels on' until you get how the indexer (and generally how CNC) works.

-B

[bill.young]

hey John,

[disclaimer. This is strictly theory..consider it a starting point]

I would first look at the available rpm's of the lathe and how they relate to the REAL cutting speed...how fast the material is moving past the bit. If you multiply the diameter of the blank by PI (3.14159) and then by the revolutions per second (RPS) of the lathe (which is rpm/60), you'll find out how fast the material will be moving past the bit. Think of this as the speed that you would be moving the bit through the material if it was laid flat and you were making a straight cut. Remember that this motion will be perpendicular to the motion of the tool, though, so it's not like you'll be trying to push the ShopBot this fast. It will give you an idea of what the bit's going to have to be cutting, though.

Diameter * PI * RPS = "virtual" cutting speed through material

Try some different lathe speeds until you get something reasonable for that "material speed" value, then you can use that RPS value to calculate the move speed of the ShopBot.

The other value you'll need to decide on is the stepover, the distance that the bit would move down the length of the blank for each revolution of the blank. That would be the amount of material that was constantly being cut off the blank, just as if it was a long straight cut. Don't have a clue what that should be...I guess it depends on the power of your lathe, the kind of bit you're using, the material your cutting, and the depth of cut for each pass, how smooth of a cut you're looking for. Remember that the smaller this number is, the less bite the bit is taking on each revolution. I'd suggest starting small and shallow and increasing as you feel comfortable

Now take the RPS of your lathe that you decided on earlier and multiply it by the stepover value that you want and you should get the speed that the ShopBot should be moving down the blank...the move speed setting for your ShopBot.

(rpm/60) * stepover = ShopBot speed value (MS)

Once again this is all theory but I think it will give an idea what will be happening at different settings...hopefully someone will chime in with some "real" experience. My vote is to start slow and speed up if it seems safe (and don't stand in the line of fire in the beginning!)

Bill

[bill.young]

(Brady's idea about using foam in the beginning is a very good one!)

[waynelocke]

You could use the Indexer tools as Brady suggested. Without the stepper I would assume that the software would run the file and show the B axis turning although nothing would really be happening.

You could also just write a file that would begin, oddly enough, at the beginning and just have a J3 move, such as J3,36,,-1. This would taper the piece from 3" diameter to 1/2" diameter in 36". If you zeroed the Z 1" above the finished diameter, you could begin with a small stepdown in the fillin sheet and adjust the speed with the keyboard to what sounded right as the file ran.

If you are starting with a square, then you are only going to be nipping the corners and will have to watch out and adjust for tearing out large splinters.

You should have all of the practice rounds you need to experiment with on the first piece and then be ready to go on the next ones.

Bill's advice and formulas seem like a good starting point. I would also use no more than a 1/2" bit and maybe 1/4".

Wayne

[waynec]

I have a Legacy Ornamental mill, which uses a router to mill many things including tapered columns. Whether or not there is computer control the problem of feed and cutting depth is the same.

The Legacy tapers columns by slanting the bed that holds the stock. The lathe ends are on a bed that can be slanted. The router cuts at a constant depth while the tilted stock rotates beneath the cutter. The fixed pitch of the drive screw determines the stepover, which is about 1/4" per revolution. If lots of stock needs to be removed, as in short steep tapers, you just make multiple passes, with some passes maybe not removing any at all on one end.

I assume you'd have to rotate a straight toolpath in Artcam, so that the rotated path would create a straight column, leaving the tapering to the slanted bed.

Always a way.

Wayne from White Salmon

[gene]

I too have a legacy and it is so simple to taper a collum . Basically the bed is slanted and the cutter the same one i use to surface my table with rides level and creates the taper. I have done 8" x 6" over 60 " on the mill and used them in a bath remodel job

[myxpykalix]

Wayne and Gene,
I don't recall seeing you on the legacy forum. Do you know about this?:
http://groups.google.com/group/Legacy-Ornamental-Mills
I too have a legacy 900 and my only complaint is bed length. That is why i got an indexer with my shopbot. Do you have any pictures of projects you made with the legacy?

[knedert]

Folks:
Sadly, we have been unable to use the Indexer tool like suggested:
"If I wanted to create a tapered column, I would create an angled line in PW, Insignia or ArtCAM and use the Indexer utilities to make that profile into a rotary file."
Because we don't have the Indexer stepper motor.... the Bot control panel locks up and crashes.... I am trying a work-around.... but would LOVE to have an easy way....
Anybody out there with a lathe and Shopbot - but no Indexer have any suggestions????
Thanks in advance,
Rose