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Self feeding/regulating tools

mookins

Plastic
Joined
Apr 10, 2009
Location
Victoria, Australia
Hi everyone,

Back with another odd problem.
Trying to cut grooves in steel pipes which are irregular. The boss hastily went and purchased a machine from the manufacturer; paid nearly $26,000AUD for it and it is absolute rubbish.
I won't even get into the details of why it is rubbish because it makes me so angry just thinking about the stupid thing.

Anyway, I am going to make my own cutting head to attach to our horizontal boring machine to do the job. I have a few options in terms of driving the tool into the work piece. Keep in mind the cutting tool must track the irregular OD of the pipe therefore will be some type of spring loaded mechanism.

First is the traditional way of having a rigid lead screw and slide assembly plunge the tool and a cut is made. The tracking assembly would move this whole part and an ratcheting mechanism would feed the tool to a depth.
I can work with that pretty easily although working out how to get an accurate depth stop might prove tricky.

Second idea is taken from how the grooving machine cuts. This machine uses a leaf spring to apply pressure to the cutting tool which then under pressure, takes a cut at whatever depth I presume an equilibrium is reached.
Does anyone have any thoughts and/or experience or even some actual papers/training manuals etc on cutting tools designed with this cutting method in mind?

Of all the problems with this machine, this cutting technique works surprisingly well and a static depth stop in relation to the cutting tool tip ensures repeatable groove depths.

I do however, have a gut feeling that tooling life may be reduced when using this cutting method as you can't control with a large amount of accuracy how deep the cut is to be made for a specific feed rate.

Any ideas or help would be greatly appreciated.

-Mike
 
I have to say, I don't have many ideas for this. But one of these came instantly to mind.

Amazon.com: Back to Basics A505 - Peel Away Apple Peeler: Everything Else

They use a spring to apply pressure but the cutter is also dragged at a low angle. The rake angle and relief on the cutter helps to regulate the cutting depth. Some have a flat surface immediately leading the cutter that "surfs" on the uncut surface contours.

It's not clear to me if you are cutting grooves around the circumference or axially along the length or on the ID or OD. Perhaps you could have a spring loaded cutter that also has a guide roller tied to it in close proximity that will follow the surface contours.
 
If you are making victaulic groves they need to be id concentric.

Drive with an id collet and cut grove with a form tool.
 
James:
Rake angle and relief geometry help regulate the cutting depth; I find that interesting. Actually thinking about it, that makes sense.
If the cutter is pivoting around an axis set up by the leaf spring, then if it goes in too far, the relief angle will push the tool back out of the cut, if it rides too high the rake will pull it back in. When they reach equilibrium the depth of cut will be set.

Heavey Metal:
Yeah they are Victaulic grooves (ES type). We are using welded pipe which has a very consistent wall thickness and will keep us within the tolerance band for the groove diameter.
So being concentric on OD or ID I think isn't an issue; the manufacturer tool which I was describing tracks from the OD.
However you raise an interesting point because I hope to use a CNC machine in the future to do grooving and knowing which of the circumferences is more important would be useful whilst setting up.
On edit: I realised what you mean by ID collet now. Unfortunately these are not straight lengths of pipe but hot induction formed bends, therefore the tooling must rotate around the pipe. Bends make everything so much harder.
 
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Never could get a sto bought cutter to work but the roller kind work pretty good in steel pipe< sq40

I think those floating cutter heads are for ali and pvc pipe.

If your mill has a facing slide you should be able to use it or a facing head or build a star drive cutter.
 
Heavey Metal:
Apparently this machine we have should cut DN200 Sch 80 pipe no worries (8" NPS Sch 80) in carbon steel.
With carbide tip inserts it will do cast also (apparently).

Tri Tool do floating head cutters fot their range of OD tracking clam shell style bevelling and severing machines. Tri Tool however only use a spring force to preload a roller against the material.
The tool is still positively driven from a slide connected rigidly to the roller, thereby giving good control on the feed depth and rate. These systems typically use a star sprocket which hits a tripping pin which incrementally drives the feed every rotation.
In these tools, the tool geometry is like any other.

With the Victaulic grooving unit however, I am unsure of whether any special tooling is needed since the tool is always pressed into contact with the workpiece by a spring force. There is no control over feed, just how the tool self regulates its cutting depths to which I am unsure of whether there are any considerations that are known that is given to such tooling setups. Are there special reliefs which can help stop the tool from plunging etc.
 
Are you after consistent depth of cut relative to the outside surface? Or consistent thickness of pipe from the bottom of the cut to the inside surface. (Seems like it would be the second one, to me.) A machine that registers with a (stationary) internal collet, holding the arm and head of a Bridgeport on an accurate 360-degree pivoting bearing would be a good start. (I'm assuming pipe diameter of 2' - arbitrarily.) Probably worm gear for rotation. "Tilt" the head/choose the cutter so the correct shape groove is produced. This would remove the variable of OD, weld "bumps", etc. from the equation... although you may have to alter rotational speed of the whole assembly if things get significantly thicker at some point around the cut.

Maybe this is a job for one of those "robot as mill" machines, in that the same machine will handle the next unusual task with only programming changes...

Chip
 
What you need is a hydraulic tracer set up, with the template stylus mounted very near the cutting tool.

If cutting with a saw, collars can be fitted. Compliance is needed somewhere.
A roller rest with one member constructed as pressure pad, and the cutting tool then located adjacent to a fixed support. Visualize centerless grinding.
 
Victaulic "specifications" that I have, don't mention whether concentricity is to be maintained between the OD or ID. The comment made by Heavey Metal about the ID being more important has some merit as the "groove depth" is given as a reference dimension. The OD however must still be within a tolerance band which I believe is tighter the the pipe specification. This is so the actual Victaulic coupling can fit over it correctly.

Chip Chester:
The weld bump is more of an issue on the inside of the pipe. With modern electric resistance welding and scarfing, the OD is left pretty much unnoticeable whereas the ID has a very slight mound with a scallop in it. It is nothing like SAW pipe which these days is only used for special sizes and/or materials or larger sizes (DN600/24") and above.

Your idea is something I have thought about for bevelling and grooving, but by the time we stuff about with all the fabricating, I would sooner just buy an old horizontal machining centre (~$30,000AUD). It would be sized to handle the pipe we require. It would do a probe cycle, a mathematical analysis of the pipe shape then generate a G-code program which will then "virtually trace" the pipe OD and cut a groove, bevel, whatever. This will only work well on a typically sized machining center for smaller pipes as the material is usually attached to at least one moving axis. Since we can bend up to 36" pipe, movement of the material is not viable without a lot of stuffing about.
I have found a supplier in China that makes a "short" travelling column milling machine. I have attached a picture of the actual machine in use in China. This is our long term game plan.

As for a robot; I want one! I only just convinced my boss (yestereve -> yesterday evening??) to do a CNC retrofit to our milling machine (this is to prove the principle mentioned above).
I am trying to convince him to get a second hand welding robot so that I get up to speed with robots; then at the next chance "Hey boss, a robot would be perfect for this application and guess what? I can program them already. Let's get rolling!". That's the plan. Results may differ.

CalG:
Hydraulic tracing is an interesting idea. It is something I never actually looked into before but it may provide a much nicer solution that spring preloading. I have used pneumatic preloading before which worked quite well. This was for peeling coating however and can be read about here.

My current design it to make a spring preload head for our horizontal boring machine. It will be similar to the TriTool OD tracking module here. The manual has a full breakdown of the parts etc. Might be of interest to someone.
 
I am at home now, but I will endeavour to upload some CAD screenshots and some pictures of the actual tool tomorrow. Most things are working well.
There are some issues however. The depth stop pin, being just a ground pin, digs in and galls the very soft material (approximately equivalent to 1018). I will have to increase its diameter to reduce the surface pressure and hopefully alleviate this problem. Other options are a roller wheel however it needs to be adjustable for depth and space is at a premium. Will research this more thoroughly.
Secondly the cut is pretty rough. Lots of galling. This is because of the soft material as mentioned before. Reading more on the forums, increasing surface speed should help as well as sharp tooling. Not sure if they mean a nice sharp edge or increased rake. Will have to do some trials and see how it goes. Already using lots of cutting fluid.

-Mikey
 








 
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