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-   Cutting various materials - bit selection, feeds, speeds (http://www.mechmate.com/forums/forumdisplay.php?f=82)
-   -   Compression spiral LEFT hand bits (http://www.mechmate.com/forums/showthread.php?t=3517)

danilom Wed 21 September 2011 09:06

Compression spiral LEFT hand bits
 
Anyone ever used left hand bits?

Would there be a problem with nut going loose from cutting in opposite direction?
I found some really nice compression bits but are left handed. as I plan to cut in one pass with them there would be a lot of force.
Spinning the spindle in ccw direction is no problem with VFD.

Got a lot of orders for cutting laminated chipboard (melamine both sides) and as I could not make the perfect cut with either straight bit or spiral had to turn them down.

Saw some advice about using two bits, down and up spiral one after another, but how well it would end up, a little of backlash or something and you got a ruined 50$ board

domino11 Wed 21 September 2011 10:08

You can use a compression spiral for that job. It has upcut on bottom of bit profile and downcut on the top. You have to cut in a single pass for it to work, but you were going to do that anyway.

Copmression Bits from Centurian Tools

These are an example from around here. You should be able to find them in your neck of the woods as well.

smreish Wed 21 September 2011 10:12

A compression bit is typical for the doublesided cutting your require. If you want to do a tool change, you can use a standard bit to cut the material in a few passes to clear the part, then use the compression bit to cut a FULL height pass, removing a very small amount of material for a finished chip free reveal. This is best done with a vac holddown, but can be done with tabs and such if needed.

Summary, if you have a 4" x 4" part, you over cut the part to 4.1" x 4.1" with a standard (cheap) bit with as many passes as required for speed, then use the compression cutter to finalize the 4" x 4" part at an optimized rate

Good luck

danilom Wed 21 September 2011 10:14

My question is mainly concerning the :

Would there be a problem with nut going loose from cutting in opposite direction?
as the tool I found is to be spin in CCW direction

domino11 Wed 21 September 2011 10:17

I have not cut anything with a ccw bit before. Cannot say I have even seen any for sale. Guess I didnt read the post clearly. :o

Gerald D Wed 21 September 2011 10:23

I think you will be okay to cut left-hand (spindle running opposite to normal). The nuts of the spindle do not carry the torque, they are just locking nuts.

In the 60's, a lot of cars had their left side wheels attached with left hand screws, but they don't bother with this today. (Chrysler, VW Beetle I remember in particular)

Gerald D Wed 21 September 2011 10:31

My father wouldn't let me touch the BMW's and Merc's at that age, but they also had left threads on the left wheels.

smreish Wed 21 September 2011 11:06

I miss understood your question. I have a Bridgeport mill with an ER-20 collet that is right threaded. I run it both in CW and CCW all the time with left and right spiraled bits. I haven't found an issue with it unlocking. Of course, I am running at 100 to 3600 RPM, not 12,000 to 24000 RPM.

danilom Wed 21 September 2011 14:05

We will see. will get back to you with results once the bits arrive to me.

ger21 Wed 21 September 2011 17:25

When we use LH bits in an ATC spindle, we use left handed tool holders with left handed threads. If they weren't needed, then they wouldn't make em. :)

Gerald D Thu 22 September 2011 00:24

Ger, we know that people make them, and probably charge a premium for them, but have you seen one come loose when it goes the wrong way? Sometimes people make them because they can :)

What is Danilom's risk if he does some experimenting in this area? Cutter stops spinning while machine continues to try and move.......we have have other things that can also cause that, but it doesn't prevent us from actually using our machines.

With the HSD spindles that we have, the main bearing retainer is held in with a left-handed nut. If the bearing seizes then it will tend to tighten the nut. HSD does sell CCW rotating spindles and I guess they change the direction of this thread. But I can't recall offhand having seen LeftHand collet nuts anywhere and I wonder if the collets ever go LH?

ger21 Sat 24 September 2011 20:04

Quote:
Originally Posted by Gerald D View Post
Ger, we know that people make them, and probably charge a premium for them, but have you seen one come loose when it goes the wrong way?
I've never used one, so can't answer that.


Quote:
Originally Posted by Gerald D View Post
But I can't recall offhand having seen LeftHand collet nuts anywhere and I wonder if the collets ever go LH?
The toolholders I mentioned have LH nuts on them. The nut is what makes them left handed.

These toolholders use ball bearing nuts which allow both LH AND RH operation. I've never seen one, though.

As you said, worst case is that the bit comes loose. It would probably break if it stops spinning. I guess if it does come loose, it's possible that the nut could unscrew and the nut and collet could fly out??

Gerald D Sun 25 September 2011 01:10

I once had a bad experience with a nut coming loose (but it wasn't a spindle)

It was a handheld angle grinder with a fancy braking system that stopped the motor as soon as the trigger was released. Sounds good in principle, but with a heavy tipped blade in there, the inertia of the blade wheel kept it spinning and loosening the nut.....then the blade would spin for about 10 seconds behind the nut while I prayed that the nut wouldn't come right off the shaft :eek:.


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