Is offset and a roughing cut a sensible way to avoid tear out with template routing?

[julianf]

As per the title.

Ive watched a number of youtube videos suggesting that as much material should be removed prior to routing, with a bandsaw etc, but no videos advocating an offset roughing cut on a router.

Why is this? It would be simple enough to do by using an oversized bearing, so there must be a reason why its not done?


Im asking from the point of view of someone who does not have a bandsaw....

Thank you.

 

[EddyCurrent]

It's common practice with CNC machining to leave a small "Roughing Clearance" then take a final "Finishing Cut".
When cutting wood I get a better finish using a "Climb Cut" for the finishing cut.

 

[julianf]

My work is cnc cutting alloy... I always leave 0.25mm on the job, and then take it off with the finishing pass.

My knowledge and skill with wood is much closer to beginner level!

But, yes, in the absence of other feeds of information, that is probably what id do on a manual router table - its just ive not seen anyone else doing it in that way (in my somewhat limited research!) which cautions me.

 

[Doug B]

Have you a jigsaw @julianf that you could hog the waste out with? As you seem to appreciate with your cnc’ing you get a better finish with a light finishing cut.
I can see no reason why using a larger bearing for initial cuts wouldn’t also work, it could just be slow progress depending on how much needed removing.

 

[deema]

Interesting, on a spindle moulder I cut to full depth when ever possible. If I take two cuts, the finish isn’t as good. I would have thought that a router just didn’t have sufficient power and stiffness to take a decent depth of cut.

 

[Phil Pascoe]

I often route an edge before sanding the surface, then again on the same depth setting- that slight difference gives a nice clean finish. This works only with the shape in one plane such as an ovolo - you can't drop the height of an ogee, for example. I often run an ogee, bullnose or edge reed around the edge before refining it from the saw, then refine the edge on which the bearing runs before the final cut - it saves work, as the work with a spokeshave or whatever only needs to be done on a narrow strip and not the full width of the edge.

 

[julianf]

Have you a jigsaw @julianf that you could hog the waste out with? As you seem to appreciate with your cnc’ing you get a better finish with a light finishing cut.
I can see no reason why using a larger bearing for initial cuts wouldn’t also work, it could just be slow progress depending on how much needed removing.

With the cnc, its not the depth of depth of cut really, but (i think, as in i know the practice, but not the thoery!) the chip removal.

When youre routing a cut through somthing, youre cutting on 50% of the circumferance. I guess thats going to be more of evreyting - heat, waste, more issues with chip clearence etc.

But a finishing cut of quarter of a mm - well, for starters its going to clean up any burr from the plunge, and then you can whizz round and just dimension everything.

Speaking of which, if theres a batch that needs a critical size, you can keep a tool just for finishing. Tools ware, and their dimensions change, so a low stress finishing tool will keep the dimensioning consistent, rather than constantly reconfiguring the offsets.


Ive got an ancient jigsaw from way back when pendulum cuts were not a thing.

 

[julianf]

Interesting, on a spindle moulder I cut to full depth when ever possible. If I take two cuts, the finish isn’t as good. I would have thought that a router just didn’t have sufficient power and stiffness to take a decent depth of cut.

I know nothing, or at least close to it... All im going by is youtube experts! : )

 

[novocaine]

straight fluted cutter unlike on an end mill, which means a clearance cut could still rip out a massive chunk and ruin your work.
I will normally cut with a saw to 2mm of the line (approximately) the let the router remove the rest, 2mm is enough that the router has a nice clearing for chips which aren't ejected upwards by the profile of the cutting edge. climb milling with a router will often leave a better finish but can really rip out the grain if you are going against it.

obviously none of this matters for metal, grain doesn't really exist (ok it does, but a microscopic level that isn't going to result in huge issues).

 

[julianf]

The next question...

On the cnc machine, for wood, ive been using this sort of thing -

But, (and again, i dont really know what im doing with wood) my cutter failure rate is significant. Im cutting to about 18mm in 2mm passes, and its always when they get deep that i get issues - they fracture at the end of the shank / start of the cutter.


The cnc is slow as well, which is why i want to move onto template work on a manual table.


These seem to be well rated on youtube (or ones of similar design). Theyre about £40 a hit, but look way more durable than the cutters ive been sending to cutter grave yard above.

Im wanting to be cutting 18mm oak.

The router is a triton tra001 (arrived this morning) Ive yet to build the table, but, at the moment, im really thinking ill just get a bit of steel plate and use that. I know it wont be as flat as cast etc. but, realistically, an amateur golfer really doesnt need a £2k set of clubs either!

 

[EddyCurrent]

For cnc these are the type I use now, long lasting, excellent finish, zero breaks yet, running at about 18000 RPM
https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313&_nkw=131842185879&_sacat=0My spindle has an ER 25 chuck so I use a 6mm collet.

 

[Phil Pascoe]

1/ buy your cutters from Wealden, and
2/ if the groove is anything like deep, plunge the cutter several times so that the waste is taken out by a straight plunge before you work the length of the groove to clean the sides. Assuming of course the cutter has a bottom cut, which most decent ones have.

I ordered a cutter from Wealden yesterday and got it in less than twenty four hours. Kent to W. Cornwall.

 

[julianf]

For cnc these are the type I use now, long lasting, excellent finish, zero breaks yet, running at about 18000 RPM
https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313&_nkw=131842185879&_sacat=0My spindle has an ER 25 chuck so I use a 6mm collet.

Thank you, ill give them a go, once i can work out the dimensions.

The ad is a bit slim on data - i mean i can buy

8mm
8mm x 75mm
8mm x 150mm

...but who knows what all that means! Im thinking 8mm has got to be the shank and cutter diameter, but then it gets a little hazy.

Can you enlighten me from your experience at all? Im wanting a flute length of around 25mm ish. 20 at a push.

Thank you.

 

[julianf]

1/ buy your cutters from Wealden, and
2/ if the groove is anything like deep, plunge the cutter several times so that the waste is taken out by a straight plunge before you work the length of the groove to clean the sides. Assuming of course the cutter has a bottom cut, which most decent ones have.

I ordered a cutter from Wealden yesterday and got it in less than twenty four hours. Kent to W. Cornwall.

Ive not actually been having any issues at all on the plunge. Its been whilst the job is just cutting normally.
The only one where i knew what happened was when it was clearing the inside of a triangular shape and it moved into the corner, and it broke then. But even then it wasnt anything significant, and the cutters that i uses for metal would not have snapped.

Its always at the bottom of the shank in the same place, where the carbide starts. Ill try some of the ones that Eddy mentions above, but, really, im hoping to ditch the cnc for the wood anyway, as its just slow in comparison to what i think it achievable with a standard router in a table.

 

[Woody2Shoes]

As per the title.

Ive watched a number of youtube videos suggesting that as much material should be removed prior to routing, with a bandsaw etc, but no videos advocating an offset roughing cut on a router.

Why is this? It would be simple enough to do by using an oversized bearing, so there must be a reason why its not done?


Im asking from the point of view of someone who does not have a bandsaw....

Thank you.

I dimly recall Custard telling us that he puts blue tape on the template when template routing, the first pass, then removing the tape for a final second pass.
PS Ideally, you should trim off all but a few mm of the waste.

 

[FranWood]

I used to do this a lot when template routing acrylic sheets. I would use a 3/8" bit with a 1/2" bearing on which leaves 1/16" of stock on. I would then remove this last 1/16" with a standard 1/2" flush trim bit. I actually have a video of this from some years back:



Normally I would locate the piece right in one corner to minimise wasted material but this video was just to show someone how I plunged though sheets at full cutter diameter. I used to polish the edges of parts once finished and plunging the bit through used to leave an uneven edge which took a while to polish out. Using the finishing cutter left a much more uniform edge that took less time to polish out.

If I was making a bunch of parts I would stick two or three sheets of acrylic together, template route them with the roughing bit, stick some more pieces to the stack and rough them out and rinse and repeat this until the stack height was the full length of the finishing cutter (~25mm). I would then send the finish cutter round the whole stack which left a nice uniform finish on all of the pieces. I could then polish the sides of al of the pieces at the same time using a sanding block as I had a much wider piece of material(s) to work with.

Now, a laser would have made this 1000x easier, if only!

 

[EddyCurrent]

Thank you, ill give them a go, once i can work out the dimensions.

The ad is a bit slim on data - i mean i can buy

8mm
8mm x 75mm
8mm x 150mm

...but who knows what all that means! Im thinking 8mm has got to be the shank and cutter diameter, but then it gets a little hazy.

Can you enlighten me from your experience at all? Im wanting a flute length of around 25mm ish. 20 at a push.

Thank you.

If you scroll down that ebay page in the link there is a table.

CUT DIA = diamter of the actual cutting part.
S DIA = shank diameter
FL = flute length
OAL = overall length, flutes length+shank length.

CUT DIA​	S DIA​	FL​	OAL​
1.0MM​	4MM​	3MM​	50MM​
1.5MM​	4MM​	5MM​	50MM​
2.0MM​	4MM​	6MM​	50MM​
3.0MM​	4MM​	8MM​	50MM​
4.0MM​	4MM​	11MM​	50MM​
5.0MM​	6MM​	13MM​	50MM​
6.0MM​	6MM​	15MM​	50MM​
8.0MM​	8MM​	20MM​	60MM​
10MM​	10MM​	25MM​	75MM​
12MM​	12MM​	30MM​	75MM​
16MM​	16MM​	40MM​	100MM​
20MM​	20MM​	40MM​	100MM​

Because the shank diameter with some tools is the same as flute diamter it's possible to cut deeper than flute length as long as you don't try to take one deep cut. The 6mm ones are my usual choice but if you look at other suppliers they also come with longer flutes and an OAL of 75mm and 100mm
In my fixed 1/2 router I use an ER20 chuck with a 1/2" shank that's fits the collet. This allows ER20 collets to be used for any size tool up to about 13mm

 

[julianf]

If you scroll down that ebay page in the link there is a table.

Im somewhat in denial here... I even went to the bother of mailing the seller, and, as you say, the table was right there all along!?!?!

Totally my error. Somewhat concerning... : S

 

[Amateur]

I think an Axminster course would be good for you. They run different courses and for all levels.
There are fundamentals you need to acquire from looking at your posts.

 

[julianf]

I think an Axminster course would be good for you. They run different courses and for all levels.
There are fundamentals you need to acquire from looking at your posts.

You are probably right, but it's the wrong biological climate for me to be travelling between towns to stand about with a load of other people.

I mean I've probably left our village less than ten times in the past year!

I do, however, have a friend who is and has always been a professional joiner (mainly hardwood window frames) whom I'm sure would advise when everyone is slightly more mobile again.

Most of what I do ends up in a good result as I'm fussy, but just takes me too long, due to lack of understanding of proper technique.