Spiral groove cut on cylinder with straight saw blade

[jeff4136]

I'm not sure I can contribute to a solution, but am wondering (and trying to
get a better grasp on the concepts)....

I <believe> that if the groove is equal to blade section (assumed a
rectangle) that a "ribbon" surface (section normal to axis) swept along the
helix and offset half blade thk each way will describe the groove side
surfaces. These intersected with a cylinder equal to groove bottom diameter
and the cylinder OD will accurately describe the groove. This is a method
I've used to model a groove cut by an end mill, believe it to be an accurate
representation and think it possible it might work for the saw cut (?).

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[rogeryang]

Hi all,
We do not have pro/manufacturing here but would like to create the groove
in subject simulating a machining process.
The cylindrical parting is turning and with a linear axial feeding at the
same time while a straight reciprocating saw is cutting the cylinder at an
angle to form the groove. The "Helical Sweep" function can not generate
the correct geometry. It appears that Surfaces may be needed for this.
I would really appreciate if anyone with similar experiences would help us
out. I will post a summary if there are enough responses and interests.
Thanks,

Roger Yang
HUSCO International

[dakeb]

Roger,

This is a very bad idea in practise.

If I understand you correctly you are cutting a helical groove in a bar with
a saw. If so you are in danger of bending or breaking the blade on both the
forward and backstroke of the saw, especially if you don't stop the axial
and rotational feed of the bar during the stroke of the saw. At best the saw
blade will deflect during the cut, making the groove an irregular shape. On
the other hand, if you stop the axial and rotational feed of the bar during
the saw stroke, you will not get a perfectly circular groove.

I think you can model the theoretical groove section with a helical 'vee'
section sweep:- \_/ . The width of the top of the groove should equal the
horizontal distance between where the blade enters the circumference of the
bar and where the blade leaves the circumference of the bar, with the saw at
the depth of the cut. This will depend on the speed of the axial and
rotational feed. The dimension of the bottom of the groove will be
calculated the same way, but at the circumference of the bottom of the
groove.

If the saw is set at a certain angle to the axis of the bar, the helical
section could roughly be rectangular.

I must say unless you have a relatively strong saw blade that will not
deflect under the sideways forces during the cut, and the groove quality
need not be good, you should not attempt this method.

Dave

[BrentDrysdale]

Hi,
I do not agree completely with David Bower.

I am assuming that the saw cut on the bar is from a horizontal milling type
situation where the saw stays in one location (and rotates) while the bar is fed
longitudinally rotating under it. If this is the case then the slot will be
wider at the top than at the bottom of the groove due to the radius of the saw
(as David suggests) but the sides will not be a straight "V". Instead the sides
will be slightly curved, from memory the form will be the opposite to a gear
tooth.

If it was me I would make an assy of the bar and saw and look at it to determine
the form of the slot. It may be that there are settings in helical sweep that
will then allow you to replicate this or otherwise as you initially suggested
constructed using surfaces (probably some swept blend stuff).

--
Regards
Brent Drysdale
Mechanical Designer
Tait Electronics
New Zealand