How to make a band cutting mandrel

[drf256]

If youre that fast at a lathe, a mandrel is a waste.

More for guys without your talents.

 

[huskihl]

If youre that fast at a lathe, a mandrel is a waste.

More for guys without your talents.

Yep. Takes me 45 minutes to get one lined up in a 4 jaw. Getting quicker every time though

 

[GoBigBlue1984]

It gets quicker with time, when I first started lining up base plates with a cylinder it prolly took 45 minutes. I'll indicate the back side of the cylinder (chamber end) first, using the 4 jaw. Loosen/tighten the nuts on the base to bring it close to .0 runout for starters then go back and do the back side again cuz it's usually gonna knock it out .010-.015 and come back and indicate the base end of the cylinder. For good measure go back and check the back side once more. Sometimes it takes 3-4 times of doing that, sometimes not. I primarily run a lathe day in day out so let's just say I get a ton of practice.

 

[czar800]

My not so pro way to sand the base... I've only done my own saws this way. It works, but like was mentioned earlier very hard to keep it even.

 

[mdavlee]

I've not cut a band on a lathe that was a good cylinder. I did one junk cylinder and started on the good one and give up and made another mandrel. Usually every 2 whole turns is around .005" out.

 

[GoBigBlue1984]

The depth of the slot for the tool bit along with shim stock could be used to control depth of cut and amount of material taken off. Use a stack up and gradually add shims till desired depth is reached. Is that how you guys do it?

Another member inquired about having me make him one. In actuality you could make one mandrel with set screws into the slot with different size sleeves and just adjust your tool bit accordingly. Think of the adjustment in a fly cutter. Same principle.

 

[czar800]

 

[GoBigBlue1984]

W

View attachment 27088

Whats your cutter angle?

 

[jmssaws]

I cut most every band flat.

 

[GoBigBlue1984]

The angle of the cutter. Not the band itself.
It looks like a sharp 90 degrees. Hard to tell from the pic. I wonder how it'd do with some rake on the back side.

 

[GoBigBlue1984]

I've given this some thought, I'll post some sketches along with the general idea a little later today when I get some time. Basically one mandrel, a series of sleeves and a collar (depth stop for cuts) and no one will need a lathe anymore for cutting squish bands. Lol

 

[czar800]

I cut the band flat.

 

[huskihl]

The angle of the cutter. Not the band itself.
It looks like a sharp 90 degrees. Hard to tell from the pic. I wonder how it'd do with some rake on the back side.

On mine, I cut the slot flat, and I used a flap wheel on my angle grinder and just relieved the backside top of the hss cutter for a bit of clearance angle. The end of the cutter was already on an angle so I left it. Works good. I tried at first having a flat cutting angle (the whole top of the bit hitting the squishband). It worked, but was slow and not consistent.

The depth of the slot for the tool bit along with shim stock could be used to control depth of cut and amount of material taken off. Use a stack up and gradually add shims till desired depth is reached. Is that how you guys do it?

Another member inquired about having me make him one. In actuality you could make one mandrel with set screws into the slot with different size sleeves and just adjust your tool bit accordingly. Think of the adjustment in a fly cutter. Same principle.

I tried it that way at first; using one mandrel for different sized jugs. The problem is keeping the cylinder square while rotating it. If your jug is much bigger than the mandrel, and you push the jug down and away into the cutter, if the bottom of the jug moves 2 or 3mm more than the top, the squish band won't be flat and it'll dig in deeper on the point of the cutter. But 3 set screws in the mandrel at the bottom of the cylinder could keep the cylinder square if you could keep them ftom getting into the lower transfers.

If you kept the cutter in the same spot (say .001"?) bigger than the mandrel, and used the same mandrel for several different sized jugs, it's hard (but possible) to not leave a ridge. You'd have to hold the cylinder perfectly straight up and down over the mandrel without wobble while turning the cylinder.

Sorry. I'm a long-winded and confusing SOB today. Mah baaaaad

*edited for fat finger typos

 

[srcarr52]

It gets quicker with time, when I first started lining up base plates with a cylinder it prolly took 45 minutes. I'll indicate the back side of the cylinder (chamber end) first, using the 4 jaw. Loosen/tighten the nuts on the base to bring it close to .0 runout for starters then go back and do the back side again cuz it's usually gonna knock it out .010-.015 and come back and indicate the base end of the cylinder. For good measure go back and check the back side once more. Sometimes it takes 3-4 times of doing that, sometimes not. I primarily run a lathe day in day out so let's just say I get a ton of practice.

It takes me 5 minutes to dial a cylinder in.

1) I bolt it to the plate in the 4 jaw and use then adjust the 4 jaw to rough in the outside of the cylinder. I'm just trying to get it withing 0.200" run out here.
2) Then I run the test indicator up and back down the bore in the gap between the transfer port and exhaust port. Adjust the clamp bolts/studs until there is no run out, here you are squaring the cylinder to the X of the lathe.
3) Turn cylinder to other side of exhaust port and repeat.
3+) If you can run up/down the intake side without hitting the transfer you can do both sides to adjust for cylinder taper.
4) Once the cylinder is square to the X of the lathe then I put the test indicator up towards the squish band and adjust the 4 jaw to remove run out there while spinning the chuck by hand.
5) Then check the outside of the bore, it's usually off a 0.010" or so from moving the jaws.
6) You can run up and down the bore again if it's way far off (go back to step 2) or just iterate run out at TDC and BDC like you would normally do (back to step 4).

 

[czar800]

W

Whats your cutter angle?

I didn't make the mandrel, but I would say about 2-3* hope the pictures help.

 

[czar800]

 

[huskihl]

*edit again...sleeves would work and fix the above mentioned problems

 

[mdavlee]

I shim my cutter up so there's some angle on the cutter both ways.

 

[srcarr52]

I cut most every band flat.

I cut them at 2deg.

 

[jmssaws]

I cut them at 2deg.

How many thousands from edge to edge is 2deg?