Need Help!- Acrilic V carved

[Jalex]

Hi all:

I have done a slightly reduced machine ( Joe2006 at 80 % ) myself and I´m testing different materials and speeds.

Trying to do a v carved letter got what is shown on the pic.
Left side is somehow scalloped , right sides are not showing this problem.

Can any of you tell me what may the cause be ?
Have tested several tool speeds, feed speeds and tool shapes , all with this nasty effect.

Thanks for your help.

[acondit]

Originally Posted by Jalex Hi all: I have done a slightly reduced machine ( Joe2006 at 80 % ) myself and I´m testing different materials and speeds. Trying to do a v carved letter got what is shown on the pic. Left side is somehow scalloped , right sides are not showing this problem. Can any of you tell me what may the cause be ? Have tested several tool speeds, feed speeds and tool shapes , all with this nasty effect. Thanks for your help.

Jalex,

I don't know for sure, but my initial guess would be backlash. As the machine cuts up one side it is pushing with the screw keeping out any backlash effect but as it cuts down the other side it is retracting with the screw and thus allowing the cutter to push back to the extent of the backlash (thus creating the scallop).

Alan

[bp092]

Looks like chatter, poor chip too. I've only cut plastics esp plexi with an oflute. What kind of plexi is it?

[Jalex]

Originally Posted by bp092 Looks like chatter, poor chip too. I've only cut plastics esp plexi with an oflute. What kind of plexi is it?

Hi bp092:
i don´t know exactly the type. It is called acrilic locally by the sign makers. This is a scrap piece i got from them ( transparent, with a plastic film on both sides ) use by them for several jobs in signs.

Jalex

[SCRAPWOTSCRAP]

Looks like multiple issues, might be extruded acrylic versus cast. The melt on extruded acrylic will weld to your bit and make quite a mess. Cast acrylic is a must for engraving. Also, you're quite deep, I might make several passes at that , last one being a cleanup pass. Might want to lower your RPM's a bit.
I've had some good luck with some Amana bits made for acrylic, here is a link .

http://routerbitworld.com/Amana_4573...37;2045731.htm

[Jalex]

Hi Alan:

I thought it was backlash too, and made 2 new nuts ( x and y ) with delrin and a very tight fit. Now i can say there is no backlash on both axis. But the pic was taken after the change... and the problem is still there.

May be the tool support is flexing ( on the x direction ) while it moves Y ...
All the machine is made in MDF. Really dont know what to do !

Thanks for your answers.
Jalex

I don't know for sure, but my initial guess would be backlash. As the machine cuts up one side it is pushing with the screw keeping out any backlash effect but as it cuts down the other side it is retracting with the screw and thus allowing the cutter to push back to the extent of the backlash (thus creating the scallop). Alan

[Jalex]

Hi :

This is a 3/16 inch acrylic and that was carved about 1/8 or a little more by 4 passes. I made also a speed control unit and am pretty shure it is not melting the material. And the problem is on one side and not in the other one.
Backlash, vibration, flexing tool support... but cant find it.

Thanks for your help.
Jalex

Originally Posted by SCRAPWOTSCRAP Looks like multiple issues, might be extruded acrylic versus cast. The melt on extruded acrylic will weld to your bit and make quite a mess. Cast acrylic is a must for engraving. Also, you're quite deep, I might make several passes at that , last one being a cleanup pass. Might want to lower your RPM's a bit. I've had some good luck with some Amana bits made for acrylic, here is a link . http://routerbitworld.com/Amana_4573...na%2045731.htm

[beone]

this is almost undoubtedly tool (holder) flex. try a light finishing pass

[acondit]

Originally Posted by Jalex Hi Alan: I thought it was backlash too, and made 2 new nuts ( x and y ) with delrin and a very tight fit. Now i can say there is no backlash on both axis. But the pic was taken after the change... and the problem is still there. May be the tool support is flexing ( on the x direction ) while it moves Y ... All the machine is made in MDF. Really dont know what to do ! Thanks for your answers. Jalex

Jalex,

The nuts are not the only places where you can have backlash. You can also have backlash where the screw passes through the bearings.

If you have a dial indicator, you might put a piece of 1/4" rod in the router chuck, and set up the dial indicator aligned with the x axis against the rod. Then grab a hold of the bottom of the router, then push and pull in alignment with the dial indicator and see how much movement you get. Then move the setup 90° (aligned with the y axis) and try the same thing in those directions. Once you see how much flex or movement you are getting, you can begin to try and find where the flexing or movement is taking place.

Alan

[joecnc2006]

Yes, my guess is your Z-Axis is Flexing, try adding some angle on the outside of the Z-Axis back plats and wrap the other infront of the plate, meaning one angle will be on side bolted and the other will make a 90deg. and be infront of the plate, make holes to rebolt tool holder side brackets back on.

Joe

[lovebugjunkie]

I had the same thing happen to me but on a much smaller scale. I was using a 1/8 bit.

I thought my feed rate might be to fast for my router (Ryobi trim) so I slowed it down which seemed to clear up the problem. Still don’t understand why in one direction it was ok and the other not.

[joecnc2006]

Originally Posted by lovebugjunkie I had the same thing happen to me but on a much smaller scale. I was using a 1/8 bit. I thought my feed rate might be to fast for my router (Ryobi trim) so I slowed it down which seemed to clear up the problem. Still don’t understand why in one direction it was ok and the other not.

maybe conventional cutting versus climb cutting.