Thread: safety - bit shaft depth in collet

I just did a quick survey of my bits

CMT and Freud have 25 mm long shafts (one of each sampled)

Whiteside has 33 mm

Carbi-Tool has around 37 mm

I can't say how much shaft needs to be seated in the collet. One thing that I can say is that they should not bottom out in the collet recess...pull them up 3mm or so from bottoming out, as that portion of bore is probably radiused, and the bit may contact it which introduces inaccuracies and vibration*

*or so I have read, at least.

It makes sense to me that the total depth of the collet should be clamping the shaft of the bit. If your collet is 30mm, I'd think that becomes the target depth of the bit.

Your plunge router should plunge further than what you describe. The collet nut should protrude from the base when at full depth, or nearly so.

Hi Mick

I looked through my books and found only one reference in Ian Kirby's book.

He says that for the sake of safety the shank (shaft) should be at least 1/2" (12.7 mm) inside the collet.

niki

not pushing it to the bottom is to seat and tighten it properly. the reason is as you tighten tne collet nut, you are pulling the collet in, and thererofer the shaft as well, which means it won't tighten properly. Hope that makes sense. you normally only need to raise it a fraction.

remove the nut and the collet and have a look at how long the collet is, i.e. the bit that grips the shaft. You need at least that much in.

The collet nut should plunge to almost the full depth, less maybe 5 - 10 mm. Check to make sure that you don't have any stops in the way.

Measure the shaft of your bits at let us know (cheapies are often short)

A photo of the bit on its own and the router at full plunge would help. A picture tells a 1000 words.

I allow 20mm min in the collet.

Cheapo bits often have shortish shafts which can be a pain if you're light on plunge.

Originally Posted by gregoryq

One thing that I can say is that they should not bottom out in the collet recess...pull them up 3mm or so from bottoming out, as that portion of bore is probably radiused, and the bit may contact it which introduces inaccuracies and vibration*

*or so I have read, at least.

Dunno about the radiused bottom. My principal reason for pulling up 2-3mm is to facilitate removal. When engaged good 'n' tight, the collet taper won't let go; need to rap inward (softly with a lump of scrap wood) to move opposite the taper and release.

Joe

Thanks to all for the replies.

Both my cheapo sets have shafts of 29mm. To get the full amount of my Ogee bit exposed (ie: below the plate) when fully plunged, I need to leave 12mm out of the shaft, leaving approx 17mm in the router.

I checked more closely my two other routers and both 'did better' than my main hand held one. I guess that is one of the things about buying cheap eBay tools (however, in my limited use so far, it has been good).

My conclusion is that 17mm should be OK but I'll be wary of pushing it too hard. I'll also check the length of the Collet and if I buy more bits, I'll make sure they have a shaft of at least 30mm.

I'll try to get a photo and post it (I only have the camera on my phone) but I don't know how to do those nice arrows like Niki does!

Note to Niki - I've seen some of your other posts and they are excellent!

Thanks again to everyone. I must say it is such a joy to have a community of people who help out. I hope that soon I'll be able to provide as much help as I have received!

cheers

Mick

Hi Mick...

This discussion was bothering me, so I dug out the manual for my Bosch router (a miracle itself after all these years).

Anyway...the collet that I have is 16mm deep, and the manual instructs the user to insert the bit at least 20mm into the collet.

Too bad the router manufacturer's design shortcut left you with this shortcoming.

Something additional.........

2 issues here,

Firstly, bit security. If you have any more than the collet length in the collet, it will have no effect on the holding power. Anything "behind" the collet will have no contribution to this,.

However, the more length you have protruding from the router, imposes other forces. Any play in the bearings is magnified; any deflection from flex in the shaft is magnified; any out of balance or out of true bit head ditto. Worse for larger bits, like panel raisers, worse at higher speeds.

Consequence is vibration.
This will affect quality of cut; could cause tool to grab?
Vibration could also work collet loose??? Have had this happen, but not sure if collet properly tightened.
Will also play havoc with bearings if sustained.

My view, put as deep into the collet, (without bottoming) as possible for the job in hand. Protrude further as necessary, up to minimum of collet length, provided none of above applies. Use light cuts and lower speed if applicable. Check collet security regularly.

"Longer shaft" bits are only a solution within the restrictions above.

My 2 bits

Alistair,

I agree with everything you say but.........

with a Roman Ogee 'cut' on the edge of a table, I will either need to do it all in one pass (simplest but of course has the issues you mentioned) or work out how I can do multiple passes where the first ones don't 'interfere' with the final one ie: all intermediate passes can NOT cut into anything further than the final one will cut. This will be a challenge (at least for me) but certainly makes alot of sense.

Thinking about it, the multiple passes will also help with avoiding any tearout at both the start and end of the top.

I nearly started using a single cut last night but am now glad I have waited as it give me something else to consider.

cheers

Mick

Hi Mick

The advantage of a single pass is that you can clamp on a sacrificial piece to prevent chipout on exit from the endgrain. That said, I have done a number, and due to size of router, (underpowered) have had to do them in multiple passes with incremental plunge. RO profile should allow this, (at least mine does).

Chipout is a problem, but take light cuts, and do the endgrain first, then you have greatest chance of removing chipout when you do the long grain. My biggest issue was router burn, with a single (high) speed, underpowered machine in hard wood(oak). I hate sanding.

Good luck

You can do multiple passes if your router has a fence. Set the fence so that the bit's bearing does not contact the work, then re-set for subsequent cuts. Either that or get a bigger bearing for the bit to prevent a full depth cut for the first pass.

If you do use the router's fence, longer timber faces can be fitted, which makes for added stability as you approach a corner of the board. I like faces on the fence to be at least 300mm long so that I can keep a good reference to the work.

Greg

Alistair and Greg,

thanks for the further information. I have a fence and to me that makes doing it nice and slowly an easy option. I also understand about a sacrificial piece at the beginning and end to help with avoiding tearout.

Alistair,

in your comment below I did not really understand about the endgrain. Based on using a plunge router (hand held) I can not see how I have any choice which way I route - I have to go from left to right to avoid tearout/kickback.

'Chipout is a problem, but take light cuts, and do the endgrain first, then you have greatest chance of removing chipout when you do the long grain.'

cheers

Mick

When routing with the grain, when you exit, you don't tend to chip out--- maybe a fringe of fibres.

If you do both ends completely first, rather than working sequentially round the piece, the chipout you DEFINITELY will get at exiting the end grain, should hopefully take place in the bits still to be removed on the other 2 sides, and should disappear when you later rout them, (hopefully with minimal chip, as in 1st para)

Thinking laterally, re previous post, I also cannot see why one couldn't clamp or glue sacrificial blocks at the crossgrain exit as well, then cut or plane them off before routing along the grain.

Another way to reduce chip out is to route the end grain first. But start at the wrong end. feed teh router very carfully and slowly the wrong way. Only do this a a very short distance 5 -1 0 mm. It will want to grab and run along. the route correctly