Well you have probably 400 grain for the cutter. Its not brass and lead
like the bullet so it is going to be larger on the size to weight ratio.
Then a 200 grain bullet is probably going to be coming out of a more
powerful gun with a muzzle velocity of about 15 to 20 times more speed than
the molding head cutter.
What do you think? The object is 2 or 3 times heavier but 15 to 20 time
Don't you think he'd notice if there was a cutter missing?
In fact, there is such a thing as a one-cutter head. Sears used to sell
one, but it seems they don't any more. It's not perfectly circular; there are
strategically-placed flat spots to keep it balanced.
Somebody sold one on eBay recently:
Pic shows both 1-blade and 3-blade Sears molding heads.
FWIW... I've never heard of a 2-cutter molding head. All I've ever seen is 1-
and 3-cutter heads.
Doug Miller (alphageek at milmac dot com)
Having done a lot of moulding work over the years I would not touch a single
cutter cutter head on that type of setup. I would sit down and scrape the
mould by hand using no more than a blunt butter knife rather than use it. It
is possible that the head may be balanced with a counterweight opposite the
knife. The only problem with this theory is how do you compensate for
different size/shape/projection/weight knives? I can not imagine how but
maybe the head is designed with a depth limiter to limit feed rates. If it
is not you are talking a major risk of kickback at that diameter and speed.
Although not a recomended practice but an accepted practice is to use
different shaped cutters on the same head at times on spindals (shapers).
Occasionally for a one of run you might only grind 1 knife and just use a
blank on the opposite side. Whenever I do this I always have a rubber lined
1/4" plate guard between me and the cutters. The rubber is to catch the
chips of the end of the cutter when it hits the guard. Even the ammount of
knife projection has a marked effect on the inbalance.On a spindle we are
only talking about a 3" head running on very heavy bearings and shaft
compared to the 8" you are talking on a TS on relativly light bearings and
smaller shaft. A spindle running collars runs at around 4000rpm, 4500 is
the maximum recomended for that type of cutter. That gives a spindle cutter
a surface speed of 4,188'/Min (4,712'/Min at max) allowing 1/2" projection
for cutter. Assuming 8" moulding head on TS you are looking at
7,200'/Min.surface speed with no cutter projection. On a spindle even if the
knives are roughly the same size the ammount of vibration due to the
inbalance is incredible. And needless to say the risk of throwing a knife
and kickback increases dramaticly as well as lower quality finish. I used to
have the formula for working out the inbalance taking centrifigal force into
account but forget it now. Maybe someone else in here can shed dome light on
that subject. I know I for one would be interested in knowing it again.
Every hour, every day I am learning more.
The more I learn the less I know about before.
After doing that for several days on end, you might reconsider using the
single cutter design. LOL
If you have never seen one in operation, don't knock it.
Tthe counter ballance is more likely engenereed to be dynamically balanced
like car tires are balanced. Counter balance weights are spread over an
averaged out area in multiple spots so that minor variations are not so
significant. Typical wheel weights on automobiles are placed in as many as
4 locations to off set the heavy spot when tires are staticly palanced. If
a single weight is thrown off the unbalanced effect is much less dramatic
than if a single weight is thrown off opposite the heavy spot.
The only problem with this theory is how do you compensate for
Size and shape will not have any effect on balance if the cutter unit is
balanced. Balance on a spinning object concerns weight, not shape or size.
I strontly suspect that different shaped cutters made ofr a single head
cutter will be shorter or longer so that different profiles each has equal
mass regardless of shape.
You would not want to run the cutter head with out a cutter in it or a 3
cutter head with only 1 or 2 cutters in it.
This would be a totally different situation and while it may be accepted,
that is truely throwing the cutter head out of balance by introducing
different weights in other locations.
Again, if the single cutter is balanced the load on the bearings is a non
A spindle running collars runs at around 4000rpm, 4500 is
Again, a single cutter head cutter will be balanced so vibration will not be
as great as you make it out to be.
A cutter does not have to be perfecetly symetrical to be balanced.
And needless to say the risk of throwing a knife
While I'll bite at the possiblilty of a kick back providing your feed rate
is "much faster" than recomended , the increase chance of throwing a knife
is non existant when copmpared to a 3, 12 , or 90 tooth cutter.
Think about single flute router bits that spin at 25,000 rpm. It's all
about balance when it comes to spinning irregular shaped objects.
Doubt it I have lots of patients and besides if its achoice between somthing
taking a long time or having the hands to do it with, the hands wins hands
Its asicly the same as set of collars with one knife and one blank except
The only practical option i see here that might wirk to allow for differing
weights/projections would be a fluid filled head working on the same
principle as an. automatic transmition torque converter,You must also
remember that increasing projection also upsets balance.
I strongly disagree here. Change the weight or the amount of projection and
you affect balance considerably. For a spinning object to balance it must be
balanced at that particular configeration. Change that configeration and you
upset the balance.
Even at equal mass if one cutter projects further than another it will
So is changing the one cutter in a single cutter head
that is true IF a single cutter is balanced.
Unless it has some form of dynamic balancing that will 'adjust' itself on
the run it will not balance with varying knives
No it does not. I have some knives which are different but designed to run
as a pair. But the design of knives in this situation takes considerable
design considerations taking into account weight distribution in relation to
projection to compensate for varying shapes and centrifigal force.
Sorry I do not follow your point there. The increased risk of throwing a
knife is due to the inbalance, nothing to do with the number of knives
Thats right ... weight is distributed equally in any direction from centre,
bit is balanced although oposing sides are different. Now lets take that
same router bit and grind or break half the carbide tip of ( simulating
changing cutter shape) ...... woops what happened to that perfectly balanced
No, I would say that the cutter head is weighted to compensate for the
weight of a cutter and all cutters for that head are of the same weight.
Increasing projection will up set balance if the changing
projection remains the same weight.
Correct if the projection changes after the balance has been made. Differnt
projections would have to be made heavier or lighter to compensate for their
Correct. That is why the cutter with another projection would have to be
made lighter or heavier to maintain the blaance. Add or take away length.
Ok, you are assuming that all cutters for the single cutter head are not
tuned for that particular cutter head.
This cutter head that we are discussing has been around for a long time.
There have been no complaints of there being a vibration or balance problem
that I have ever heard of. This is not all theory, the tools exist and run
with out exagerated vibration.
We are both beating our heads against a brick wall here. ;~)
The tool exists and has for many years. Apparently it works.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.