[Mountaincraft]

Have a brand new plastics bit... My only one (had an 1/8" one but immediately broke it because of wrong feeds and speeds)

Amana Tool 51404 Solid Carbide Spiral 'O' Flute, Mirror Finish, Plastic Cutting 1/4 Dia x 3/4 Cut Height x 1/4 Inch Shank Up-Cut Router Bit

Gotta cut a couple circles in 1/4" acrylic today...

Have 'no idea' where to set feeds and speeds and DOC...

Suggestions of a good safe starting point?....

[fizzissist]

Why not post what your "wrong" feeds and speeds were that you believe caused the failure?

Acrylic is a whole lot softer than cutters, so if it breaks, it's 99% of the time chips sticking to the cutter and/or not clearing, so it's a mechanical failure.
THE very first thing you want to do is make sure you've got good air flow at the tool/material interface to keep the material from melting onto the tool and to clear the chips. Flood coolant works fine too.

[txcncman]

Problem I always have with plastics is melting. Heat is cause by friction. Reduce friction you reduce melting.

[fizzissist]

I can't imagine that using the speeds and feeds for HSS on aluminum wouldn't work as a very safe and conservative starting point along with good air flow for cooling and chip clearance.
It's worked for me in the plastic jobs I've done where I'm making a model in plastic and then a part...without having to post twice.

[pointcloud]

Just use a 1/4" drill? It'll make a circle. Lol..

[ger21]

10,000 rpm and 80-100 ipm.

[Mountaincraft]

10,000 rpm and 80-100 ipm.

Thanks Gerry... Cut the whole 1/4" DOC in one pass, or should I split it up into two passes?

[ger21]

I'd say make 2 passes until you get a feel for it.

[Mountaincraft]

I'd say make 2 passes until you get a feel for it.

Cool thanks.. What I was planning on doing anyways if I got no reply in time...

thanks!
:cheers:

[ssutton]

I have cut a LOT of plastics and acrylic sheet this year. The one thing that got me to success consistently with all types of bits/speeds/feeds was to put air cooling (shop compressed air) blowing directly on the bit. Not only does this cool the tool but more importantly it totally clears any chips from recirculating back around into the tool and melting. I set up my router so that the tiny brass air line is part of the vacuum hood. I have a needle valve installed to adjust the air volume. I will post a pic in a few.

Scott

[ssutton]

The setup works like such. When the router comes on the 110VAC that turns on the router also energizes an air valve that starts the cooling air flowing to the tool. The brass tube is pinched down to deliver a high velocity stream of air to the tool. The brass valve controls the air volume. The same 110VAC turns on the 2HP dust collector machine so that it all starts/stops when Mach turns on the spindle output. This setup has proven VITAL to cutting sheet aluminum as well as plastics. The aluminum plate attached to the router in the first pic is a vinyl cutting attachment, I remove the dust collector when I am vinyl cutting.

Scott

[LouF]

Mark I cut my Acrylic at 8000 rpm 100 in per minute feed rate and I do it in two passes and I use tabs..


Lou

[Mountaincraft]

Mark I cut my Acrylic at 8000 rpm 100 in per minute feed rate and I do it in two passes and I use tabs..


Lou

Tabs would be problematic for this as the piece has pockets on both sides and as such has to fit perfectly into a workholder cut out for the reverse side pockets....

I'm gonna be trying this double sided tape I got for the first time that a local plastics shop recommended to me... they used to use it with their CNC rig before they went to laser... Dang tape costs a small fortune....

if it works (and a quick test taping the acrylic down says it will), then it will save me 'loads' of time and hassle on a product I want to do production runs with....

[LouF]

Tabs would be problematic for this as the piece has pockets on both sides and as such has to fit perfectly into a workholder cut out for the reverse side pockets....

I'm gonna be trying this double sided tape I got for the first time that a local plastics shop recommended to me... they used to use it with their CNC rig before they went to laser... Dang tape costs a small fortune....

if it works (and a quick test taping the acrylic down says it will), then it will save me 'loads' of time and hassle on a product I want to do production runs with....

I should have said I have used the tape with good results. I have cut some only the protective film was keeping it in place with out anything holding it.


Lou

[louieatienza]

I would say if you're using a 1/8" bit you probably don't want to go more than 1/8" a pass. I also use the same bits. If they still don't work you can try a slow-spiral or up-shear bit, it will help break up the stringy acrylic chips.

Anothier thing is to make sure your Z axis is trammed perfectly plumb, otherwise the bit will rub on one side. I like the idea of the air blast as well, though haven't had the need. You also need to crank the feed up or slow the spindle down, or a combination of the two. If you're going to do a big run you might want to consider making a makeshift vacuum jig to hold the parts down.

[Mountaincraft]

I would say if you're using a 1/8" bit you probably don't want to go more than 1/8" a pass. I also use the same bits. If they still don't work you can try a slow-spiral or up-shear bit, it will help break up the stringy acrylic chips.

Anothier thing is to make sure your Z axis is trammed perfectly plumb, otherwise the bit will rub on one side. I like the idea of the air blast as well, though haven't had the need. You also need to crank the feed up or slow the spindle down, or a combination of the two. If you're going to do a big run you might want to consider making a makeshift vacuum jig to hold the parts down.

I'm planning on adding air when I rebuild the table.. but it's not gonna happen now... The router gets too hot for too little work, and I believe that much of it has to do with the 'vacuum system' we all need to use.. I also believe it has to do with the fact that I messed with the 'plate' that was used to hold the factory speed control that came with the router.. and replaced it with my own that mounted the SPID optics.......

I want to force cool air through the router to alleviate all of this...

the bit is a 1/4" diameter. the first one that I broke way back when I first got the table fired up was a 1/8th inch...

vacuum table? who knows.. hoping to have a smaller laser table up and running before I have to go that route... but ya never know....

[louieatienza]

I'm planning on adding air when I rebuild the table.. but it's not gonna happen now... The router gets too hot for too little work, and I believe that much of it has to do with the 'vacuum system' we all need to use.. I also believe it has to do with the fact that I messed with the 'plate' that was used to hold the factory speed control that came with the router.. and replaced it with my own that mounted the SPID optics.......

I want to force cool air through the router to alleviate all of this...

the bit is a 1/4" diameter. the first one that I broke way back when I first got the table fired up was a 1/8th inch...

vacuum table? who knows.. hoping to have a smaller laser table up and running before I have to go that route... but ya never know....

Aside from my RotoZip, I've never had a router heat up excessively, and I've run jobs over 12 hours long. I don't know if it's the vacuum system since I've seen machines here both with dust boots that shroud the router, and those isolated from the router exhaust, without problems. Most likely the bearings may be getting overloaded or the SPID is pumping a lot of juice to the router, because it's trying to fight through the molten plastic. I just made new dust boots for my machine, using a Kyocera 1/8" spiral-o-flute to cut both the 1/2" HDPE base in three passes, and the 1/4" acrylic window in one pass, with no issues (and without the new SPID sensor attached).

Point is, I don't see how forcing air through the router would alleviate a potential blockage caused by your optics bracket; a redesign of the bracket may be in order. Also, it could be that your particular router just doesn't push the rated HP, and you might just have to crank down the feedrate and/or doc to accomodate this (I had a PC router that seemed to be this way.)

I made a makeshift vacuum fixture a while back using scrap MDF which I sealed with shellac, and door seal from the hardware store, ran with my ShopVac. Not ideal, but it worked just fine for a quickie production run....

[ger21]

I also don't see how the vacuum could be making your router hotter??? I would expect that if the router were turned off, and the Z axis lowered until the brushes touch the table, that the vacuum would actually pull some air through the router itself.
Unless you have a really unusual setup, I'd say that the vacuum has nothing to do with your hot router.

Also, the Super PID should make the router run cooler, as it's more efficient that the standard speed control.

As Louie says, unless you're pushing it really hard, you either have a bad bearing, or the airflow inside the router is really restricted.
I can run my PC 690 all day and it barely gets warm at 13,000 rpm or less.

Even when I crank it up to 16,000 when I use really small bits for carving, it won't get anywhere near hot even after 3-4 hours of use.

From my experience, after 5-10 minutes, it should be about as hot as it's going to get. If it keeps getting hotter after that, then something is wrong.

[Mountaincraft]

The router body does not get hot at all.. but after running it for a bit on aggressive cuts (ie profiling through wood), then the collet/router shaft gets pretty hot... almost too hot to touch... and the shaft will 'squeak' when turned as I'm tightening the next bit in... give it a few minutes to cool down and it doesn't squeak...

Doesn't appear to be any run out or wear issues... Who knows.. maybe I got a funky one.... that happens to me a lot.. LOL

It'll last till I get the rebuild done and go to a bigger router or spindle....

[ger21]

Sounds like a bad bottom bearing.