Spiral milling in a circular pocket

[mattpatt]

If I use the 2D pocket milling in a circular pocket, the toolpath is a bunch of concentric circles. What I want is a spiral from the centre out.

I believe that SC2011 will have this option, but for now I had to have a fiddle.

In other CAM software they have this option, such as mastercam, but what I had to do was this:

Now my pocket is basically a 66mm through hole. The part is 10mm thick. I drilled out the centre just a shade bigger than my cutter and then used an HSM strategy.

I used HSM - Spiral Milling. I made a surface in the CAM part which basically blanks off the bottom of this through hole, and I can use that as a 'virtual' bottom of the hole and gives me something to select as the target part.

The 66mm diameter is my constraint boundary. Tool on working area is 'internal'. Z depth limits are set just so that the tool doesn't move off the bottom of the hole.

After fine tuning here and there the tool slides into the centre hole that I drilled and then spirals out to the 66mm diameter with constant tool engagement.

Only trouble is that as soon as the tool hits this 66mm diameter it pulls out and doesn't complete the circle. This is a bit of a shame but not a huge thing as I can then come in again with a 2D profile strategy to get the job done.

Does anyone have any other idea as to how to do this?

Cheers,

Matt.

[Brakeman Bob]

This is something I never have to do on our parts (the holes in those are small and long) but I can see that it would be very useful for machining those bigger holes. Have you tried doing it as a Profile job and setting the technology as Roughing and cearing an offset, perhaps with the cutting set to troichoidal. There is also a setting on that page for making the cutter complete a Z level before moving on to the next.

Another way of doing it would be to work out the logic for an approximation of a spiral and then putting that in the post as a drill job. I saw something like that some years ago in a different life but it would be a bit a job though.

[mattpatt]

Well, I've had a good play today and I've made some progress. Not with the Fadal, but with the Haas.

First off, I usually use pocket milling, and have also tried a profile with clear offset as Bob mentions, but it still wasn't what I wanted.

I've had a look at building a spiral and it would be a task! Certainly not impossible but I'd have to sit and play with it first for a long while until I got it figured out.

Anyway, seeing as my Haas uses a G13 for circular pocket I thought that I'd mess around with the gpp file to set this up.

G13 (and G12) have 2 options, either roughing with a spiral out to the circle diameter, or just fnishing at the circle diameter. Both starting from the centre.

So for my Haas MAC file I added a couple of drill jobs, one for each type of G13. These included the necessary inputs I need to make such as diameter etc.

Example:
drill_type = Circ_Pocket_Finish Drilling Y Rad_Inner_Circle Z_Feed_In XY_Feed

In the Haas GPP file I then messed around in the @drill section until I got what I needed. The code generated looks perfect, but the machine's flat out so no chance to test as yet.

While in this mood I then added deep hole drilling (G83) and deep hole chipbreaking (G73) to the drilling technology, which drills to the first set depth, then each peck gets incrementally smaller until it's at another set peck depth. Up until now I've been relying on either constant peck depth in both G83 and G73.......Not any more :-)

The data for these is added in the drill cycle data tab while setting up for the drill operation.

The @drill section is not considerably longer than it was, but everything seems to be in order. There's probably a way to clean it up, but if it ain't broke.........

[pinguS]

Just out of curiosity, if you are doing pockets, I am assuming on on aluminium, like milling out a takeaway carton, which method is best for this. Is it the pocket recognition feature, or HSM/HSS way.

Going by your post which way actually did you get it to pocket from inside out?? Did you have to specify a minimum center cut diameter, as unless you have a center cutting tool, you would have a crash?? I'm thinking off the top of my head, but I have a 400mm by 500mm carton shape to pocket out, and am not looking forward to it!!!
p.s. sorry for the partial post hijack

[mattpatt]

Many of my parts have pockets of the "take away carton" style you are talking about. Here's a rough outline as to how I attack them in 2D:

If the pocket goes al the way through then I'll simply drill a hole in the middle of the pocket, slightly larger than the endmil I'll be using to hog out the pocket, then use this drill centre as my point of entry into the pocket. Then I don't have to worry about plunging or anything like that and can go down to the next Z depth at full speed. If the corners of my pocket are, let's say a 3mm radius, but I use a 12mm endmill to clear the pocket then I'll use rest rough after the 12mm endmill to just clear the rest material. I'll use a pocket strategy on both the rough and rest rough. Finishing will be a profile strategy as I only need to finish the outsides.

If there's a bottom to my pocket I'll could use the same as above, but the depth of the pocket would be only to the point that my initial drill hole was at full diameter. The for the final depth, where the drill hole tapers away I would basically copy the first operation, but have my upper level set to the final depth of the previous op, and then use a Helical entry to the final depth. That way I'm never plunging straight into the material.

You could finish the wall and floor of the pocket by selecting the check boxes.

These are the basics, but there are many other ways.

In 3D:

The pocket would be my work area, and I would use 3D drilling to drill the initial entry hole. Then constant Z roughing to rough out the pocket, with the 3D drill operation selected as the entry point. owever, I think this will still plunge wnen it gets to the final depth, so you'll have to check that out.

In HSM:

Contour roughing would clear the pocket, and you could select any of the entry strategies such as helical, or linear etc. for a smooth entry cut in the z depth.

In my case a lot of my pockets in the parts I make have tapered walls, and are not all flat on the bottom, so I tend to use HSM countour roughing to clear the material, then possibly a rest rough to get the corners to size. Then constant Z to finish the walls and 3D constant step over to finish the floor.

If the picture attaches correctly you can see the pockets on the underside of this Aprilia RS250 top triple clamp. The floors on these pockets are very contoured, and the walls tapered 1 degree, but with some playing around with the above HSM strategies it came out just as I wanted it.

[pinguS]

Thats an excellent finish, how did you get then table to come out so orange? (joking). The parts look pretty smooth, what scallop/step over settings did you use to finish the pockets, and how long would you say it actually took them to machine, from rough to finish (mainly finish as I'm assuming that is the longest op)? Did you need to buff up the bottom of the pockets after machining?

sorry for the million questions..

[mattpatt]

My parts come off the table, get cleaned and then anodized. Under no circumstances will they be touched with an other abrasive. That's sacrilege! I can tell you the times and techniques tomorrow. Not in the office now.

Recently I made some parts for a bloke's chopper. Against my better judgement I must say. Anyway the parts where very nice then he insulted me by polishing! I refused to make the rest of his stuff. Told him to go and get chromed

[MKproto]

Here is how I do large pockets with a spiral path.

Drill your starting hole for the pocket.

Start a 3-d milling job and select the outside of your pocket as your work area and select internal. This will keep your tool inside the pocket.

- Under technology select a semifinish spriral tool path, under data enter in the parameters you want to use. (Delta is your step over)

-under finishing select constan z and pick your leadin move etc.

The draw back is the tool disengages but you get 99% of what you wanted.


Matt