Question... Help me make a good choice on a flush trim bit. I'm not just interested in which bit - I'm interested in why it's a good choice.
I'll share my thinking below so you can confirm, correct, or guide me elsewhere. But first I'll share a little context...
How I'm choosing a flush trim bit...
The questions seem to be - what brand, what diameter, what cutting length, number of flutes, what shank size, and straight vs. spiral-up/down/combination...
What brand... is addressed in many other threads on this forum. Here's what I've gleaned from them...
What diameter...
What cutting length... I've seen little or no discussion of this question, though it also seems this is an application specific issue. For a flush trim bit there's a minimum required cutting length for whatever material I'm using. Beyond that, I'd pay slightly more for longer cutting length to make it useful in a future project with thicker material. I see no disadvantage to longer cutting length beyond price, as long as the work is supported in a way that doesn't make the extra cutter protruding below the workpiece a major hazard. My current use is flush trimming 1/2" baltic birch, but I'd buy a 1" cutting length over a 1/2" for future versatility.
How many flutes... I understand that more flutes are generally better, yielding a smoother cut and allowing higher feed rates.
Shank size... I'm considering only 1/2" shank for a stronger bit. I might make exceptions and use a 1/4" shank if I needed to flush trim tight inside radius corners (I don't right now) or for cost reasons if I was buying a solid carbide spiral bit (addressed below).
Straight vs Spiral... and spiral up/down/combination...
So, which flush trim bit? I'm considering the following options from this Eagle America page. Once I narrow to a specific bit, I'll compare that precise bit against other brand choices - at least Whiteside and Freud for their many recommendations on this forum.
If money was no object, I might buy the last one - 3 flutes advantage, 2" cutting length probably exceeds anything I'l ever flush trim, and the versatility of top & bottom bearings. The only anticipated need it can't meet is tight inside radius corners which would suggest the first one - but that's not a need today.
If I ordered this moment, I'd buy #4 - or similar in another brand. It's likely I'll actually buy Freud or Whiteside because I can get Freud locally at a big box store and I can get either fast via Amazon prime. That bit choice is paying a few bucks extra for three flutes (vs #3), and getting 1" cutting length which works fine today. That's missing the opportunity for a longer cutting length for future needs, missing the benefit of top & bottom bearings... and that's ignoring the smoother cut of downshear options because I'm lacking expertise on whether it makes the router squirly.
All input is welcome.
Broader picture promised at top... besides a flush trim bit, here's what I'm buying ASAP for specific uses in current projects...
I'll share my thinking below so you can confirm, correct, or guide me elsewhere. But first I'll share a little context...
- I'm a routing newbie, reasonably experienced elsewhere in a shop, about to buy my first bits for use in a Bosch 1617, which will be handheld until I build a table (currently at least four projects down the queue).
- I'm asking about flush trim bits - just to make the question concrete - but my immediate purchase list also includes others. I'll include specific immediate routing needs at the end of this post in case it's relevant.
How I'm choosing a flush trim bit...
The questions seem to be - what brand, what diameter, what cutting length, number of flutes, what shank size, and straight vs. spiral-up/down/combination...
What brand... is addressed in many other threads on this forum. Here's what I've gleaned from them...
- Eagle American, Whiteside, Infinity, Sommerfield, CMT, Freud, Amana all seem to be top favored brands with a very slight bias toward those earlier in that list.
- MLCS seems to be the most recommended brand of the lower tier. Some here favor MLCS for less used bits and others wouldn't use them without full body shrapnel protection.
- Sommerfield has the edge for matched sets (like tongue and groove) because no height adjustment is required after changing to the second bit. Freud matched sets have fans here but I don't know whether they share that specific advantage. Neither is relevant to my current choices since my immediate purchase needs are not sets.
What diameter...
- It seems that larger diameter bits are better, as long as the router has the power to swing it... which doesn't appear to be an issue for a Bosch 1617 with a flush trim or any of the other bits I'm considering.
- Exception: if flush trimming inside corners, a smaller diameter bit may flush trim a tight corner that a larger diameter bit cannot. However, this is not an issue for my current project or for the next four projects in my queue.
What cutting length... I've seen little or no discussion of this question, though it also seems this is an application specific issue. For a flush trim bit there's a minimum required cutting length for whatever material I'm using. Beyond that, I'd pay slightly more for longer cutting length to make it useful in a future project with thicker material. I see no disadvantage to longer cutting length beyond price, as long as the work is supported in a way that doesn't make the extra cutter protruding below the workpiece a major hazard. My current use is flush trimming 1/2" baltic birch, but I'd buy a 1" cutting length over a 1/2" for future versatility.
How many flutes... I understand that more flutes are generally better, yielding a smoother cut and allowing higher feed rates.
Shank size... I'm considering only 1/2" shank for a stronger bit. I might make exceptions and use a 1/4" shank if I needed to flush trim tight inside radius corners (I don't right now) or for cost reasons if I was buying a solid carbide spiral bit (addressed below).
Straight vs Spiral... and spiral up/down/combination...
- On first look, solid carbide spiral bits seem to have significant advantages if I ignore cost. A second look shows a price difference enough to make me take notice, especially if I stay with a 1/2" shank. Even if my budget allows me to pay $70-100 for what would be $20 in a straight bit, it doesn't mean that I want to.
- My current projects are shop projects not cabinets. Materials are mostly baltic birch and dimensional lumber. I think straight bits have been successfully used with such materials for decades, so I don't think spiral is needed.
- If I buy spiral, I'll buy up-cut so the router wants to stay firmly on the work.
So, which flush trim bit? I'm considering the following options from this Eagle America page. Once I narrow to a specific bit, I'll compare that precise bit against other brand choices - at least Whiteside and Freud for their many recommendations on this forum.
- #117-0412, 2 flutes, 1/4" diameter, 1" cutting length, 2-7/16" total length, 1/4" shank, single bottom bearing, $28.95
- #117-0615, 2 flutes, 3/8" diameter, 1" cutting length, 3-1/8" total length, 1/2" shank, single bottom bearing, $17.95
- #117-0825, 2 flutes, 1/2" diameter, 1" cutting length, 3-1/4" total length, 1/2" shank, single bottom bearing, $17.95. (That's also available with downshear for $21.95, but I'm uncertain whether that makes the handheld router less stable as it would with a spiral downcut bit.)
- #117-0835, 3 flutes, 1/2" diameter, 1" cutting length, 3-1/4" total length, 1/2" shank, single bottom bearing, $21.95 here
- #117-0865, 3 flutes, 1/2" diameter, 1-1/2" cutting length, 3-5/8" total length, 1/2" shank, single bottom bearing, $25.95 (also available with 2 flutes for $19.95, #117-0855; both also available in 2" cutting lengths for about $5 more)
- #117-1215, 2 flutes, 3/4" diameter, 1" cutting length, 3" total length, 1/2" shank, single bottom bearing, downshear, $32.95 (yes, still uncertain about downshear; straight version is cheaper; longer cutting lengths available)
- #117-1215B, 2 flutes, 3/4" diameter, 1" cutting length, 3" total length, 1/2" shank, top & bottom bearings, downshear, $46.95
- #117-1305B, 3 flutes, 3/4" diameter, 2" cutting length, 4" total length, 1/2" shank, top & bottom bearings, $53.95.
If money was no object, I might buy the last one - 3 flutes advantage, 2" cutting length probably exceeds anything I'l ever flush trim, and the versatility of top & bottom bearings. The only anticipated need it can't meet is tight inside radius corners which would suggest the first one - but that's not a need today.
If I ordered this moment, I'd buy #4 - or similar in another brand. It's likely I'll actually buy Freud or Whiteside because I can get Freud locally at a big box store and I can get either fast via Amazon prime. That bit choice is paying a few bucks extra for three flutes (vs #3), and getting 1" cutting length which works fine today. That's missing the opportunity for a longer cutting length for future needs, missing the benefit of top & bottom bearings... and that's ignoring the smoother cut of downshear options because I'm lacking expertise on whether it makes the router squirly.
All input is welcome.
Broader picture promised at top... besides a flush trim bit, here's what I'm buying ASAP for specific uses in current projects...
- 1/4" straight bit, both for routing 1/4" through slots, and possibly also for routing dados using an exact width dado jig. I may consider a solid carbide spiral up-cut bit for this with a 1/4" shank, or I may stay with a basic straight bit.
- 3/4" straight bit, for routing 3/4" - 1-1/2" dados using an exact width dado jig.
- 1/8" roundover bit, for softening edges. My ROS works, but I'll use this bit enough that I'm willing to pay for it. If I was going to consider MLCS anywhere, I might consider it here and get this set for $30 vs paying the same for the single Freud bit needed now..
- (Optional)I'm considering a rabbet set. I can build what I need without it as the above straight bits are perfectly capable of cutting rabbets with the RA1154 edge guide... though the convenience is tempting.