I need a custom jig or fixture for making cylinders.

[TTalma]

I need to make cylinders of various sizes out of wood, And I am looking for a fast way to do this with a good surface finish. The cylinders would be from 6" down to 1" in diameter and from 4" to 24" long. I am using a variety of woods, but mostly Hard maple and Cherry

I have a 4th axis. I tried using a 1" flat bottom bit and rotating the blank. This made a nice cylinder but the surface didn't look great. So I tried putting a flap sander in that is designed for CNC machines. This made the surface nice and smooth but there was some burning left on the surface, due to the high speed. But it took about 7 min for the whole process.

I next tried running a long bit along the length of the side of the cylinder, doing this and rotating the blank 1 degree at a time left a nice finish and a nice look but it took 7.6 seconds for 1 pass along a 6" cylinder, it took 45 min to complete. Way to long. This was at a feed rate of 200, I could probably go faster but not much, and trim off a few min.

How can I get a nice smooth surface that looks good and feels good to the touch. Is there some sort of Jig or fixture I can make?

My machine capacity is: 32"x40"x6.52"

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[Jim Dawson]

Could I suggest that a lathe is more suited to making cylinders Routers are marginal for making cylindrical parts.

[TTalma]

That is true. I guess I should have said that areas will have carving etc. done to them. But there will be many areas that are round.

And my lathe is manual. (For now anyway !)

[he1957]

Solid carbide cutters may give a better finish.

As an aside, you could try cutter shapes (gouges etc) as used in a lathe fixed at an appropriate angle to a non-rotating mounting block (tool holder) on the gantry/spindle mount and use the machine as a vertical down-cutting (Z motion) or horizontal side-cutting (X motion) lathe. Depends on the mounting and orientation of your setup.

I've yet to try it but don't see why it won't work.

[ger21]

It likely won't work because a rotary axis is not a lathe, and is typically neither powerful enough or fast enough to work like a lathe.

Try a bowl bit running along the axis, a little off center.

[wizard]

Assuming your table is rigid enough you could go to grizzly and buy a lathe head stock modify it with a high power servo that can drive the wood at turning speeds as well as handle the engraving duties. This woiuldn't be a trivial project as finding optimal sizes for the head stock and servo will take a bit of work. Also your gantry and Z needs to be stiff enough to handle common lathe tooling. The gantry could be a significant problem here as even cheapish wood laths have fairly stiff beds. In the end the head stock turns the parts fast enough for conventional wood lathe cutting with the gantry and Z replacing the lath bed and manual tooling supports.

The second alternative is to take the same approach one would use on a large mill, that is to use tooling that can maximise material removal. Think about the difference between a 6inch shell mill and at 1/4 inch end mill. Of course this assumes having a spindle that can handle the load. You would not use a shell mill in wood of course. However you may find something off the shelf that could do the job for roughing anyways. Think large router or shaper cutters used for profiling. The problem you will likely run into here is horsepower to drive the spindle and rotate the part blank. This would also imply a cutter change between roughing and finishing.

I'm also of the opinion that a custom or semi custom cutter might be helpful. In fast I would not be surprised to find that such cutters have already been made and are marketed by someone as this does not seem like an odd requirement. Maybe a check with your tooling suppliers. If you have a large enough taper in your spindle I might suggest trying to make a custom cutter stack up.

What do I mean by custom cutter stack up? Well imagine an arbor that takes two shaper style cutters. One for bulk material removal with a second cutter mounted below for finishing cuts. Going with standard shaper cutters would allow you to expereiment with optimal cutter profiles. This may sound like out of the box thinking but years ago I saw an advertisement for an adapter to put small shapper cutters into a standard 1/2" router. 1/2" is actually pretty thin for what I think is needed here so if your spindle can handle a much larger arbor it would be highly advised. Example: https://www.mlcswoodworking.com/shop...r_collars.html, note all the qualifications and warnings. Shaper cutters come in various bore diameters and you would most certainly want to use something larger that 1/2"

There are lots of possibilities here. For example a table saw or band saw can knock off the corners of square stock haveing a massive impact on material removal requirements. in the case of your current approach this might be all you need to do.

[he1957]

Gerry, good point. Had thought of that as far as rotational speed goes. Depending on the 4th axis design perhaps it could be "modified" to allow faster rotation. Reverse pulley sizes or disconnect step/servo motor and attach regular motor for making cylinders?

[islaww]

Of course you would have to upgrade the size and increase the power, but the basics in a smaller package are here:

[TTalma]

A lot of great suggestions. I do think my headstock and tailstock on my 4th axis is pretty rigid. And I do have a 5HP spindle that takes er32 collets. But as Ger mentioned the speeds are pretty slow, I never figured it out but I would guess my max speed would be around 60 rpm. When I turn by hand on my lathe something this size I would run at about 2000 rpm.

I think wizards suggestion of the custom bit/finding a bit with a close radius is a good idea. I found a few bits on eagle america that look like they are close where I only need part of the profile. I emailed them and explained what I'm doing and to ask for the radius of some of there bits. I have had bits made before, but they are pretty expensive, so I would like to use something "off the shelf" if possible since I would need min 3 different profiles.

I think the best idea though is islaww's. This looks like the right tool for the job. But unfortunately I don't have one or the time to build one right now. It will be about another year before I'm ready to do anything like that. But I would love to have that on a larger scale.

[wizard]

It islawws idea is pretty much what I was thinking with respect to a lathe year stock mounted below the gantry.

A custom approach like this is better as you likely can achieve far more stiffness for a given investment. The real trick here is right sizing a servo for the rotary axis. Depending upon the controller and servo you may need to select an incremental node for high speed spindle usage. It nice you have everything sized correctly and then oh hAve modern hardware the machine implementation should be easy.