Need Help!- Stacking Router Collet Extensions To Make a Long Bit - Good Idea?

[NIC 77]

I've been looking at long bits for milling foam for an upcoming build with a long z-axis.

I realize there are many threads on this, however I have yet to see any posts that talk about stacking router collet extensions to get the desired bit length.

I'll be using either a super PID or a variable speed router to control the speed, haven't decided which yet, but in either case unless I'm mistaken the slowest I will be able to achieve is around 5000 rpm.

If I were to stack let's say two of these

ER Straight Shank Extensions

and put a 1/2 inch shank 3/4 inch diameter round nosed router bit on the end, I would have a bit of around 12 inches with an end bit wide enough that I wouldn't have to worry about the collets contacting the piece on long cuts.

So what does everyone think? Will this setup work for milling foam at 5000 rpm?

[ger21]

I think it would be very unsafe, but that's just my opinion.

Also, ER11 collets can only take a 1/4" shank I think.

You can get 10" long tools here.
http://3dcutting.com/products/frogtools

[NIC 77]

Originally Posted by ger21 I think it would be very unsafe, but that's just my opinion. Also, ER11 collets can only take a 1/4" shank I think. You can get 10" long tools here. Foam Cutting Tools | Foam Router Bits | FROGTools

Yes, I've had a look at frogtools already. The largest shank size I think I can fit with a router is 1/2, so their longest bit I could use is 10 inches as you mentioned, subtract an inch for mounting. That's 9 inches and $270 for just one bit.

Good point about the ER11. I was looking at a whole bunch of different collet extensions online and I did not clue into that when I made the post.

OK then how about a collet extension like this one, half inch to half inch.

Amazon.com: MLCS 9465 1/2-Inch Shank Router Collet Extension and Wrenches (router bit not included): Home Improvement

Amazon.com: MLCS 9465 1/2-Inch Shank Router Collet Extension and Wrenches (router bit not included): Home Improvement

What does everyone think about stacking a couple of this type of extension with a router bit on the end to mill foam at 5000 rpm?

Any other suggestions for extensions? Anyone know where I can get a longer half inch to half inch extension? I don't want to pay $270 for a single bit that is used for foam, and I'd like to go up to 12 inches of bit length.

Alternatively, If I could find a 6 inch long half inch to half inch extension then I could use a more reasonably priced 6 inch end mill and still have the ability to put a standard router bit on the 6 inch extension.

[silyavski]

even if it works it will screw your spindle bearings with the time. buy a spindle with low runout and the tool that's meant for the job. there are also companies/ most of them/ which can do a custom bit for you which can be cheaper than the one stated.

[TDA]

A big part of the problem is runout (wobble). You have runout at every connection (collets, extensions, and tool) and it gets worse the further from the source so that could be a LOT of runout. I personally would think it is very unsafe, bad for your router, and your cut would be larger then your tool.

To give you an idea of the issue a 4 to 1 ratio is the MAX recommend on spindle systems which are far more accurate then a router (especially with stock collets).

[NIC 77]

Originally Posted by TDA To give you an idea of the issue a 4 to 1 ratio is the MAX recommend on spindle systems which are far more accurate then a router (especially with stock collets).

Please explain what you mean. I don't understand what you're saying.

[TDA]

A 4 to 1 ratio is the MAX recommended. So as an example if you had a 1/2" shaft on an extension the max recommend length of the extension would be 2" (1/2" times 4). This is not to say that they don't make longer ones. But they are not recommended by most good dealers. The problem with the added length is that even if you have very minor about of wobble it is exacerbated by the length.

A good demonstration of this take a pen and hold it with your thumb and index finder. Now just barley rock your fingers and watch how much the tip of the pen wobbles compared to the amount of movement at your fingers. Now imagine that spinning and you get a good idea of the problem and why they don't like going very long.

[NIC 77]

OK, thanks for clarifying. That makes sense now. I thought at first you were talking about bit length and that didn't make sense.

I've given up on the idea of stacking extensions. Thanks to everyone for their input.

There's a pretty long extension being used here:

‪2010 24 enero 012.mpg‬‏ - YouTube
Maybe not ideal but it looks like it's working just fine.

I've read it posted here a few times about using a long drill bit and grinding the tip down for milling foam. I think I'm going to try that........got to build the machine first.

If that doesn't work, I'm going to get a custom bit made from somewhere or find a place to buy a long extension.

[silyavski]

It will work if you buy a brand good quality drill bit like Dormer for example. Also SKF sell precision bearing shafts and at Ebay you can find long carbide blanks. After that you have to heat treat it and temper it but basically the tempering is done in the following manner/ very generalized/. With a propane torch you heat it until red,this should be done fast, no more than 2 min or you will loose carbon from the edges. Meanwhile with a small magnet checking when the metal looses its magnetic properties. Be carefull not to touch the magnet as the magnet rapidly also looses its properties if heated, so when you reach this point when the metal is non magnetic you put it in a bucket of water in a such way that the tip enters first and from tip to end it enters for 3-4 seconds, not faster! This will make the bit hard at the top, springy at the length and soft at the end. After that you put your kitchen oven to 200 degree Celsium , clean gently the bit to shiny iron and put it inside watching it carefully. When you see a yellow oxide forming take it out and leave it to cool down naturally. Again-Yellow, if you go from yellow to other color, you have to repeat everything as it would be to soft.
if you follow correctly everything you will have a nice properly tempered bit

[NIC 77]

Originally Posted by silyavski It will work if you buy a brand good quality drill bit like Dormer for example. Also SKF sell precision bearing shafts and at Ebay you can find long carbide blanks. After that you have to heat treat it and temper it but basically the tempering is done in the following manner/ very generalized/. With a propane torch you heat it until red,this should be done fast, no more than 2 min or you will loose carbon from the edges. Meanwhile with a small magnet checking when the metal looses its magnetic properties. Be carefull not to touch the magnet as the magnet rapidly also looses its properties if heated, so when you reach this point when the metal is non magnetic you put it in a bucket of water in a such way that the tip enters first and from tip to end it enters for 3-4 seconds, not faster! This will make the bit hard at the top, springy at the length and soft at the end. After that you put your kitchen oven to 200 degree Celsium , clean gently the bit to shiny iron and put it inside watching it carefully. When you see a yellow oxide forming take it out and leave it to cool down naturally. Again-Yellow, if you go from yellow to other color, you have to repeat everything as it would be to soft. if you follow correctly everything you will have a nice properly tempered bit

Thank-you for taking the time to post some advice. I did some searching on ebay. I don't understand what you mean. What am I supposed to do with a carbide blank? Are you suggesting that it would be better for me to buy my own blank and send it somewhere to be machined into a bit, or that I try and grind a bit out of the blank myself? I just don't get it.

[silyavski]

Originally Posted by NIC 77 Thank-you for taking the time to post some advice. I did some searching on ebay. I don't understand what you mean. What am I supposed to do with a carbide blank? Are you suggesting that it would be better for me to buy my own blank and send it somewhere to be machined into a bit, or that I try and grind a bit out of the blank myself? I just don't get it.

i meant the blanks and the bearing shaft if you decide to custom shape a long bit. probably you will better go with a ready made long drill bit and filing with a diamond file by hand and or liquid cooled, as doing so you will avoid the need to temper the steel. excuse my ignorance but what bit exactly is best suited for foam?