Avoiding chipping out with a lathe

[Curt Bartel]

I need some advice on using the wood lathe with the shopbot. I am not sure how to go about cutting a spindle , but this is what I have tried and I am getting the profile I want but have a problem with my spindles not being smooth(chips and chunks coming off while cutting. I have my lathe set up parallel to the Y-axis. I draw my profile in vector then I contour tool down to half the diagonal of the spindle( e.g. 4x4 spindle diagonal measurement is 5 inches so i drop down in Z 2.5 inches) . I put my 4x4 in the lathe with the edge pointing straight up and set this edge as z=0. I then set the side edge as x=0, and cut the part stepping my z down about 1/16 at a time . My lathe is set at its slowest speed and I am using 1/4" down cut spiral bit in my variable speed porter cable router which is set at its fastest speed. I want to end up with a smooth spindle with no chips or frays. Should I be using a different router bit or should my x- move speed be set different (currently .2 ipm.) or is the way I am dropping down to slowly cut the spindle (contouring) the wrong way to do it.
Thanks in advance

[waynesutter]

Curt. I recently mounted a lathe on my shopbot and am turning out spindles that do not even need sanding. the secret is to not cut the profile with the z axis. You should cut the profile in your case with the x axis while moving in the y for the lenght of the cut. I use a long 1/2" standard two flute router bit and make a final finishing pass with minimum cut and slow speed. I would be curious about how you mounted your lathe. I mounted mine to the side of the table along the x axis. I program the profile to cut using the x and y with the z set to below zero.

If you will e-mail me at sutter@iinet.com (mailto:sutter@iinet.com) I will send you a utility I wrote to turn dowels of any diameter and any length. I worked very well for me and many others have used it as well. Since my lathe is mounted differently you will have to modify the program for your axis but this should be a simple task of exchanging x and y commands. Take a look at the projects files regarding wooden gear clocks. we had a discussion about lathe work and the use of it in the clock.

Wayne Sutter

[Gerald D]

If I read this correctly, Curt is using the tip of the cutter while Wayne uses the side of the cutter?

[imserv@imsrv.com]

Curt if you use the lathe roughing routine in Vector,it will create a series of roughing tool passes and a finish pass, always starting at the right and ending at the left of a "lathe" rotary axis mounted parallel to the X axis. It can automatically compensate for the cutter diameter

To use it with your axis aligned to the Y, create the drawing as if it were aligned to the X axis, and then Cut-Paste with a 90 degree rotation, or simply rotate the coordinate axis by 90 degrees and locate it at the place you set your zero in X & Y.

A couple of assumptions are that 1) the material is free turning (just like a real lathe) and not under CNC program positioning control , and 2)you are trying to make a part like a bowling pin, and not a fluted part with a controlled helix. 3)Cutting with the side of the cutter should produce a better finish than the cutter end, especially since you are using a down cut which will be pushing/impacting the chip right back into the cut area.

If you are trying to do 3D contouring, you should investigate the Vector rotary axis option which you would be able to use to cut with the Z and a full radius or Ball cutter. In this case the tool is no longer programmed like a lathe but becomes a controlled rotary axis, commonly referred to as a 4th axis. Complex forms, drawn in 3D are contoured with rotary motion replacing one of the linear axes (X or Y).

[Curt]

Wayne, I built the shopbot wood table and when I got my lathe I modified the table. I wanted to be able to use the lathe with the shopbot and also freehand so I mounted it to the right side of the table. I had to move one of the 2x4's (second one from the right) over so that I could fit the lathe to the table and still have room for the tool rests. I built a table for the lathe which is mounted under the shopbot table and is screwed to the shopbot table legs. I was trying to think of an easy way to raise and lower the lathe table in case I need to use the full shopbot table top but I couldn't think of an easy and convenient way to do this. The lathe is very heavy and I don't want to break my back moving it. Any ideas for raising and lowering the lathe to get it out of the way would be appreciated. I mounted the lathe parallel to the Y- axis because the spindles I am trying to reproduce are only 10.5 inches long and I didn't want to redesign a shopbot table at this time to fit the lathe parralel to the x-axis.
In regards to Gerald d. question I am cutting with the tip of the bit just like doing a cut on a flat piece of wood only I have the spinning 4x4 underneath it.

[Curt]

Thanks Fred. I will look into vector lathe roughing routine. Can anyone recommend a router bit with a 1/4" diameter that will cut a 4x4 on a lathe without the 4x4 eventually hitting the router chuck?( the bit probably needs to be about 4"inches long) Also when cutting from the side I will need that router bit to have a deep depth of cut, right?The spindle I am trying to reproduce has some fine details and I think if I use any bit larger than 1/4" that I will have to freehand the pointed cuts and I would like to avoid as much freehanding on the lathe as possible.

[imserv@imsrv.com]

Curt, you may want to rough the 4x4 with a larger tool to remove the corners, and then once it is round, change to a smaller tool for the finer details(finishing). If you are cutting from the side as was discussed, while the lathe turns, you will need a cutter that reaches just past the centerline of your lathe(in Z). A 2.6 (plus a bit) inch flute length should allow you to cut across the diagonal of your 4 x 4, which is the maximum cut depth you will need.

The Vector Lathe roughing will let you specify different radius tools for roughing and finishing.

If you have several parts to make, you can rough them all with a large tool, say 1/2, then change to the 1/4 for the final pass, changing out the parts for each tool, rather than the tools for each part.

[Curt Bartel]

I think I've got this lathe thing figured out!
After many attempts at getting a 4x4 turned without chipping out the rings and chipping out the area where the cut departs from the 4x4, this is what I came up with(any other suggestion or improvements to what I have here would be appreciated):

1)The lathe function in Vector works great.
I used a 1/4" downcut spiral bit cutting at the horizontal centerpoint of the lathe.

2)The router cuts on the downside of the spinning wood.

3)I cut from the tailstock end of the lathe to the motor end of the lathe.(Just like routing an edge of a board freehand, router is on the opposite side of the board as my body and cutting from left to right. This is backwards from normal edge freehand routing, but I think I minimized the chip out)

4) each step in cut .05"

5) speeds
Move xy = 00.15[.06]
Jog xy = 1.20[.66]
z speeds doesn't matter because there are no z-moves

6) Lathe spinning at 400-500 rpms( this is the minimum speed on my lathe)

7) router (portercable vs) full speed

When I finished shopbotting the spindles there was fuzz on them which was easily removed by rubbing my finger across it, although I just hand sanded the spindles very lightly while running them in the lathe to remove the fuzz.

I have a craftsman variable speed lathe which I mounted partially under the table in the y-direction. I made the wood table and mounted the lathe between the two 2x4's at an end of the table. I did have to move one of the 2x4's a little bit so I could still use the lathe for freehand work(e.g. touching the coves up for the fine tuning where the 1/4" downcut couldn't get into). The lathe will probably be a permanent part of my table; I don't want to move it around very much because it is so heavy.

There are 3 things that I maybe could get some suggestion on
1: dust control for a lathe(a box around the whole thing? or a vacuum setup? or other ideas?)

2: A way to move the lathe down easily in case I need to utilize the full table on my shopbot( some sort of jacks or something?)

3: Can I get 1/4" downcut spiral or similar end mills in 6" long lengths; I know there was a few words about XL bits on the Forum. Where can I get them and do they cut similar to a downcut spiral on wood? If I recall the XL bits were for metal cnc cutting.

Thank you
Curt Bartel