Hello welcome to Enots engineering I'm Alan
today I'm looking at the belt tensioner for the rotary head
this was the one in the MDF version It consisted of a bearing and a sleeve
and into this sleeve was a bush with a offset bolt hole.
so you could move the bearing in and out and this would take up the tension on the belt
this one is made for automotive for a cam belt and it's quite a big bearing
so what we're doing today I'm using the same inside which is the aluminium with the offset hole
I'm making it fit a new bearing and we're making a sleeve for the bearing
so that the belt can be held between the sides of the sleeve and run in the middle
So it will give it some guidance
so let's go to the workshop and see how we make it
so the stepper motor will come through here the pulley will be there
this was the tensioner that I used before which is far too big
I found this bearing so what I'll do is modify the offset
so that fits the bearing and once I have the belt fitted across the two
I can then position the centre hole for this so that I can put tension on the belt
it doesn't need a lot of tension being a toothed belt
so just to get this block set in the right position
I've scored a mark in the centre and I'll use the centre in the tail stock
until I can get this lined up
but for now I'll just hold it in the chuck
by using this center as a guide
I can see which way I have to move the chuck jaws to get the centre lined up with the cross
by slackening the chuck jaw one side and tightening up the jaw on the other side
I can move the centre position of the plastic so there aligns with the centre in the tailstock
I'll just adjust the plastic so it protrudes out of the chuck jaws a small amount
To allow me to face the plastic off once I've bored the hole
I'll just check that all the chuck jaws are tight before I start to machine
I've just drilled a 10 millimeter hole in the plastic for the boring tool to pass through
that's about 1.3"
I'll leave that at that size you can see it's just going in
finishes a little better
I'll leave that as it is
I've finished in the four jaw chuck
I'll swap that now for the three jaw
at the moment I'm using a parting off tool to go in and form a recess
and I'm hoping to get that recess the same width as the belt
okay I will go a bit deeper
so what diameter is this
Two Two inch
The belt fits that's okay make it a little wider on the slot
What I must do next is just puts a slight chamfer each side
so that the belt will go into the centre
I'll take that out turn around finish off the outside
so now I've just put the bearing in there
because I've machine such a lot off this
the plastic is a bit flexible the bearings gone in and it's holding
so it's only a guide the belt it won't be the teeth that go into the slot
it's going to be the back of the belt
maybe just a bit wider so there's play in there
so if it's off centre slightly I'll still do the job
so that's a tensioner
that was the old one I was using
the new one slightly smaller but it now has the proper guide for the belt
and also I want to press this in here
we've then got the offset on the cam for the tension
I will press this in in the vice
this is the back of the rotary head this is where the belt will be when I put spindle in
With the stepper motor in the corner now this is the part we've just made
this is a plastic belt guide bearing and then through the centre
I've got this aluminium piece which is an offset hole
The idea of this is it will go on to the belt to adjust the height
It will go either way
It goes on to the belt lock into the belt where then when i've set the position
I'll drill a hole through the bolt will go through the hole and hold the adjuster to the back plate.
And then by turning this on the bolt it will release tension or put more tension this belt
you can see there the difference between the MDF one the aluminium one
on the prototype the MDF is 20millimetres thick
so on the aluminium one I only need it to be 10 millimeters thick
thats reduce the height in about 20 mil and the width by the same
it's reduced my area to put the the belt
so I've got to be more accurate with the positioning of the belt
and that's why I had to redo the tensioner to make it a little bit smaller
well that's the tensioner finished
I hope you enjoyed it and we'll see you next time on
Enots engineering