Will this work or is there a better way to make this large delrin thrust washer

[TQA222]

I am using a 7 x 12 mini lathe with a 4 inch 4 jaw chuck. I will be turning a piece of 4 inch delrin bar stock approximately 2 inches thick The goal is to make a thrust washer about 4 in OD 3 in ID and maybe 3/8 thick

I would prefer to have the security of a center in the tailstock which means cutting in to the face of the piece and leaving a boss in the middle for the center

I was thinking I would start with a V shaped threading tool and make a recess about 7/16 th deep then switching to a boring bar. Will this work or am I missing something elementary. Alternatively is there a better way to tackle this?

Working on the OD if needed and parting off I am OK with.

I want to be as prepared as possible because this part is for the rudder on my boat which is also my home. Getting to it will require Lifting the boat out of the water and digging a hole under the rudder to drop the rudder.. This will take place on the small island called Carriacou.

 

[WarrenP]

Delrin cuts very easily. Usually when making a center hole you will use a drill or series of drills to make it as big as you can with drills then use a boring bar to cut to size. With the delrin 4 inches thick there shouldn't be a problem with it sticking out 2 inches from the chuck, no need for extra support.

 

[RJSakowski]

A 4" diameter rod being turned in a 7 x 12 lathe could present a problem with holding the work securely. Unlike metal, plastics have a tendency to distort easily and pull out of the chuck.

To start, I would cut a section from your stock slightly thicker than the finish thickness. You can use the four jaw and the tailstock center for this. As Warren said, Delrin cuts easily. Prior to cutting the slice, I would face the tailstock end.I would start the cut with a parting tool, taking it deep as I could and finish the cut with a hack saw. This can be done in the lathe under power of you're careful. The parting tool groove will guide your cut. As you near the center, you can finish the remainder of the cut with the lathe turned off. Alternatively, the slice could be cut with a band saw or even with a woodworking saw.

Once you have parted off your slice, you can mount it with the finished face in the jaws and indicate the disk to center it. Face the second side. Rather than bore out the entire i.d., you can use a procedure called trepanning to cut a groove slightly smaller in o.d. than your required i.d. This gives you a more rigid workpiece and you will have a 2"+ disk for another project.

I would use sharp tools and err on the side of lighter cuts to avoid pulling the work from the chuck. The trepanning tool should have enough relief so it won't drag on the cut. A 1/4" HSS tool bit can easily be ground to make the the tool. An old tap or drill shank could also be used. You will need about 10º of side relief and perhaps the same amount of end relief for 1/4" tool.

 

[mikey]

I agree that Delrin is slippery to hold and I would opt to make a tenon of reduced diameter to more solidly hold the part by and reduce the stick out of the jaws at the same time. I would make the tenon roughly as long as the jaws are deep and make the part sticking out past that tenon about 1/2" - 3/4" thick. That way, you can butt the rear of the work piece against the chuck jaws for maximum support and eliminate the need for tailstock support.

I agree with Warren. Just drill the center and bore it out from there. If you make the tenon as above, the axial cutting forces encountered as you bore will not be a problem because you have adequate support from the work piece being backed by the chuck jaws. Bore 1/2" deep and then just part it off at 3/8" and you're done. Easy.

 

[MarkM]

Throw your pc. In the chuck. Face it. Now remove and turn it around and put that new face against the chuck body. Drill it out as large as you can. Bore it, and face it. Remove and now chuck it from the inner diameter. Turn the od then part. Wall is only a half inch at this point. Parting should be no problem. Just make sure you end up being able to part your pc. And your final pc. Is clear from the jaws.
Delrin cuts real easy but not too fast as it will heat up and break your swarf by stopping your feed so it won t wrap itself around your workpc. Drills can bite into your workpc and cause it to spin in the chuck. Don t be too greedy and let the drill shear your cut. Be aware your chuck can squeeze the part. Inner jaws won t give you this problem and keep your part concentric if you turn the o.d. While your pc. Is in the inner jaws. You don t have clearance in your chuck so be aware when boring. Just keep clear and face that off after boring once turned around. Just angle your boring bar here and cut through that hole so you don t have to face off the complete face. Just get close to the hole size then face off.
Part to size. Chamfer before completing parting.

 

[Ulma Doctor]

to save material on large od work,
turn the od to dimension,
i have made gentle trepanning plunge cuts on the billet, and use a boring bar to to get the id from the trepanning cut,
and do the chamfer with a 45° tool, then use a parting tool to release the bushing/spacer, sometimes switching out the 45°tool to chamfer the other end before parting off completely

 

[TQA222]

to save material on large od work,
turn the od to dimension,
i have made gentle trepanning plunge cuts on the billet, and use a boring bar to to get the id from the trepanning cut,
and do the chamfer with a 45° tool, then use a parting tool to release the bushing/spacer, sometimes switching out the 45°tool to chamfer the other end before parting off completely

Thank you for your reply and confirming that what I was planning was OK.

My principal reason for not wanting to go for the usual drill hole the use a boring bar to create a recess was to retain the center boss with the drilled center so I can use the tailstock with a center for security.

 

[P. Waller]

Your approach works fine, this is 6" OD X 3" ID aluminum parted off 1/8" thick using a .236" wide parting insert. This method allows you to make several parts before having to bore deeper to make another

I use a plug with a center placed in a hole at the bottom of the counter bore.

Not a hobbyist quality finish on the back side but there was other back work required so I did not fuss with the tooling. Deep parting rarely leaves a nice finish because the chips are stuck in the groove. it was accurate however.

 

[Jimsehr]

I would chuck it. Drill it with a half inch drill . Then run a 1/2 13 piece of allthread thru part and spindle and then put a nut on both ends . Then turn od and trepan Id
To size. Delrin is so easy to cut you could take a 1/4 HSS tool and plunge straight into face of part to bore it to 3 inch size. You just have to sharpen end of tool and make sure you have enough clearance on trepan tool. I could make the tool in less then 10 min.

 

[P. Waller]

I would chuck it. Drill it with a half inch drill . Then run a 1/2 13 piece of allthread thru part and spindle and then put a nut on both ends . Then turn od and trepan Id
To size. Delrin is so easy to cut you could take a 1/4 HSS tool and plunge straight into face of part to bore it to 3 inch size. You just have to sharpen end of tool and make sure you have enough clearance on trepan tool. I could make the tool in less then 10 min.

This is absurd.