Ramp rates ?

[gundog]

I have been getting bad edge quality lately and just realized it coincides with my upgrade to 3.8.xx I am wondering if something changed? I have since changed my pinion gears thinking that could be it but it did not help. Could some setting have changed to cause this? I tried a new bit and get the same results. I have cut this material many times and not got this bad edge finish. Any thoughts? I hold my parts with vacuum and that has not changed I have the same vacuum pressure so that is not it.

I have never gotten great edge quality but now it is getting intolerable. I cut HDPE plastic. My machine is a 2008 PRS stadard, I just want to get it back to where it used to be. I don't know if the newer control software has anything to do with it but it seems to be about the same time I started noticing the problem.

Thanks Mike

[tom_fiddler]

Could you post a few pictures. I would like to see the before and after edge finishes.
I cut a lot of HDPE and am always looking for ways to get a better finish.

[Kyle Stapleton]

Go back to the older version and if it goes back to cutting good it was the software, if not I guess you have to keep looking.

[gerryv]

Michael,
I'm far from a Shopbot guru (chuckle) but I spent many years as a problem solving specialist/consultant for some large multi-nationals including manufacturers and I agree with your line of thinking.

To help eliminate/verify what you're considering, could you get your hands on another PC; first load up the same 3.8.XX version and run the same file from both computers and compare results - likely a quickie, edge cutting file. Then, with the older SB version loaded on the 2nd computer use the same file once again and compare cut results. All else being equal and assuming that all your setting are the same, I'd think that would go a long way towards clarifying the "is it a software or hardware" question.

That said, hopefully, someone with more SB experience will step in and say something like "reset your kididle to x.xx and all will be fine:)

[gundog]

I don't want to go back to an older version I like the new enhancements but what I am wondering is if the ramp rates changed? I have tool path templates saved that ran fine before so speeds and feeds have not changed but I notice areas that have a chattered finish that were not like that in previous jobs. I don't have pictures of previous cuts and it is hard to photograph the edge finish. The chattered finish seems to be where the tool ramps into the part. I also notice that my inside profiles look great smooth as silk so I am thinking something changed but what?
Mike

[adrianm]

Did you save your old settings before upgrading? If so you could compare them. I've got into the habit of always saving my settings and keeping them on a flash drive as I've been caught out by this situation before.

Where you running different settings to standard with the old version? If not then you could load up the old version on another computer and have a look at the settings there. The settings have changed over versions as some of the default settings in Brady's ramp article are now different from when that was written.

[jerry_stanek]

What bit do you use

[gundog]

I have never changed the ramp setting from the way the machine came in 2008 I don't know how or anything about that? I did not change the settings in the newer version of software I just loaded it and started using it. I will have a look at Brady's article and see if I can make sense of this. I think I have a saved version of the old software Bill & Randy helped me load the new stuff at a camp Shopbot held at my place this last Oct.

I use a single flute upcut 63-XXX from Onsrud designed for cutting soft plastic. I have been using these same bits for years. The problem is recent I have never gotten a perfectly smooth edge but it was tolerable now it looks much worse in certain areas and it is usually in a straight area of the cut the corners and inside profiles look really good.

I will try and take a picture but I am not sure it will show up very well. These cuts are in 1/2" HDPE Seaboard I also cut 1.250" UHMW and I gave up a long time ago trying to get a good finish in the UHMW. The parts I make in UHMW get re-machined on a lathe to fix the edge quality but the parts made in HDPE are not round and cannot be cleaned up that way.

Thanks Mike

[srwtlc]

Mike,

Aggressive or messed up ramp setting would show up in places where ramping is needed, corners/curves and start stop areas, not in straights.

Some things worth looking at are pinions and rack. You replaced your pinions, but one should also clean the rack of caked on grease with something like a brass brush. Don't put too much pressure on the motors when tightening them back up as too much pressure can cause vibration. You can hear if you have them too tight by jogging end to end and they may have a bit of a growl to them (not motors but gears). Check the rails/rollers for caked on dust etc. and buff it off with a scotch brite or 0000 steel wool with some light machine oil. Any binding on the X or Y axis. PRS Y axes can be tight due to poor adjustment of the lower v-bearings. Spindle/router bearings/collets going bad.

Sounds like maybe a build up of some situation over time.

Is your standard the 4g Gecko box? Maybe some adjustment of the drives would help. Call SBHQ on that.

[gundog]

I run 2 passes to depth on .500" Seaboard so it ramps to depth usually in the straights so it will show up that way. I have cut it in one pass but edge finish suffered so I went back to 2 passes. I made some changes to the VR settings today and I have some parts to cut in a couple days so I will see what happens.

I cut some UMHW today and I can see where it ramps to depth and is really chattering bad in those areas. This was before I made the VR changes. The ramp I made in the tool path was 2" in length with a .375" single flute bit. I am not confusing tool path ramp rates with the VR setting but I find it interesting that this is my worst area of finish.

Mike

[gundog]

I finally got around to reading Brady's article and made some changes to my ramp rates and changed my speed & feed to get my finish back to where it used to be. I have cut 3 sheets of parts from Seaboard and it is cutting satisfactory again. I notice the machine seems to be moving with less noise and more smoothly.

Mike