How to make better router cuts

[bradleyheathhays]

I'm in the process of building some molds out of 1/2" acrylic sheet and I'm using pattern pieces and a straight cut bit on my router to cut the acrylic to size (first time I've done this btw). Although I know my pattern pieces are good and straight (come from a pro cabinet maker) the acrylic ends up having little ripples on the cut face no matter how little I try to take off at a time. Since the patterns are good I guess the problems got to be with my setup.

I'm running a Dewalt DW616 1.75? HP router on a flimsy Skill RAS900 router table that weights maybe 15 lbs. and not held down. The bit set was cheap off amazon and unfortunately has a 1/4" shank.

I'm guessing I need to at least screw the router table down and use a 1/2" shank bit. Any other suggestions?

 

[jttheclockman]

Cheap is what you buy and cheap is what you get. What are the pattern pieces made from?? Do they have ripples in them?? A pattern bit will copy what the pattern is. Yes secure the table down PLEASE!!!!!! When using a router your concentration has to be 100% on the work at hand. Trying to keep a table from moving and moving a workpiece past a fast spinning bit is recipe for an accident. Yes 1/2" shank bits are many times better than 1/4" shank bits. You will get less chatter and ripples as you mention. A good sharp bit with a well oiled bearing is what you want to work with. I am a fan of Freud bits as well as Whiteside. Are you feeding the work in the right direction??? Your last cut should be smooth and with a quick pace but not pushing it. You should be shaving minimal material at that point. Nothing wrong with that router. Make sure it is locked at the height you need. One important rule with all routers, route from the same area on the base throughout the project. There are times when a bit will not center within the base ring and variances can happen. If the router is VS, make sure it is running at highest speed on finish cut. Make sure the bearing is clean and free of any adhesive or resin. Good luck.

 

[bradleyheathhays]

Thanks jt that's exactly the kind of general advice I needed to hear.

Pattern pieces made from 3/4" birch plywood and are good. Feeding from right to left. I'll work on making the improvements you suggested.

 

[duncsuss]

Thanks jt that's exactly the kind of general advice I needed to hear.

Pattern pieces made from 3/4" birch plywood and are good. Feeding from right to left. I'll work on making the improvements you suggested.

After addressing all of John's suggestions, if you still have ripples try one final pass feeding the opposite direction. I know, it's called a "climb cut" and can lead to problems if you are removing stock, as the bit will tend to climb out of the cut. But for a final clean-up pass, with basically no stock removal, it might help.

 

[GaryMGg]

Can you show your set-up after you secure the table?
How are you keeping your hands away from the cutter? What's holding the object being cut?

 

[bradleyheathhays]

Thanks duncsuss I'll keep that technique in mind and try it in future projects.

Gary I'm afraid my setup is laughable compared to professional woodworking standards. My shop area is in a bit of an upheaval right now but this should give you an idea. I'm using this silly little table with a DeWalt 616 router installed. The 1/2 " acrylic pieces I've made so far are one 5x5 in square and four 5.5 x 14 in pieces. I held them directly when cutting them down with the pattern and the table was 'heavy' enough that it didn't move. I'll end up screwing it down like I said but now that I think about it there's enough wonkyness in the table itself that securing the questionable legs probably won't do much for the small ripples I've been seeing.

 

[jttheclockman]

Now lets back up here abit. You said you are doing patterns. This means you are attaching a pattern on top of blank and now using a straight cutting bit with bearing to follow the pattern. You do not want to have to cut too much material this way so you should cut the blank very close to size before routing. You do not use the fence with this. You use a starters pin and route more or less freehand. But you need to be sure that pattern is adhered to the blank well because if it slips all hell breaks loose.

But I will take this to other levels. If these molds are square then why not cut with a tablesaw and be done with it. With the right blade you will get mirror like edges.

Then another thought is why not use the fence and run the pieces past a fixed bit for a clean pass. I would work other things out. Have no idea what you are doing now so all bets are off.

 

[bradleyheathhays]

Thanks again jt. Roger on not using the fence v. the pin and using secure double stick tape.

Reason I'm using my router to make these cuts is because my table saw is terrible. I've just set up some basic equipment and my table saw will be the first upgrade I make. Luckily my buddy has a really nice Delta waiting for me soon as I can get 220 ran to my garage, but that's down the road a little bit.

Actually using the fence and a fixed bit? is what I've been doing, I think. Router is mounted upside down in the table so I guess that's fixed.

 

[howsitwork]

It might help slightly if the table legs are under tension? By that I mean push them out slightly at the base then screw down so the top it " stretched " for want of a better way of putting it. this might address any end to end or side to side wobble a bit.

Id be tempted to use CA to stick your templates in place as, like JT said, if they move all hell breaks loose. The CA can be got off afterwards by soaking in acetone for a few hours.

 

[bradleyheathhays]

Update. I've had a lot of suggestions for a O flute upcut bit but despite all my search I don't believe there's one of these made that's designed to be a trim bit, with a guide bearing. All of them I found were meant for CNC.

The closest kind of bit I can find to what's been suggested is something like the Whiteside RS5200 1/2" shank 1/2" bearing 2" cutting surface length. If a O flute upcut can't be found would this do it?...

 

[jttheclockman]

Not needed. Your ripple effect thing is a product of operator error. If you are trying to cut all in one pass you are asking for an accident. A router is actually a more dangerous tool than a tablesaw and yet people do not see it. This is because more people use tablesaws than routers. This is hard for me to explain because I know what I am doing and I can answer my own mistakes right away. But without knowing what you are doing it is so hard to help by typed words. That router table is not a bad one. Just needs to be nailed down and if you have to splay the legs some to take the slop out of it then try that. But when you push your work past that bit that table or the bench it is mounted to should be rock solid. Takes one potential hazard out of the equation. Next is if using a pattern then you need a starter pin and not use the fence. You take small bits off till you get to about 1/64" left and that will be your final pass. You run this through without stopping and if you need to to adjust hands then step back again and run again. If your pattern has no bumps in it then the cut should be smooth. A good sharp bit will cut through plastic easily.

You can use either a top bearing or a bottom bearing flush trimming router bit. As I said I prefer 1/2" shank because it takes out the vibration when routing hard materials. I prefer Freud or Whiteside bits and they can be found from many sources. Not much more I can tell you. Maybe someone else has more. Good luck.