I made my own concave cup center with a hole in the middle when I ran into a need for one
while turning Christmas tree ornaments. It allows me to turn down the top of my Christmas ornaments
to all most nothing, before parting them off. It also allows me to sand the ornaments before parting
them off. I have access to almost all of the ornament and I don't need to worry about breaking it
I am going to use the same Hollow Concave Cup Live Center the next time I turn a finial.
My Hollow Concave Cut center is just a custom point that fits into my "Precision Machine
Revolving Center". I made it out of UHMW Polyethylene plastic. UHMW is easy to turn and a little on
the soft side. Not hard like steel. I turn a SOFT, rounded over transition into the center hole.
Rather than an abrupt hard transition. Thus, my custom point does not leave a mark on my work.
Note: You can remove the point from a Oneway Live Center. See photo below. This will create a Hollow Concave Cup. The problem, is the transition from the cup to the hole in the middle is abrupt. It has a hard steel edge, that often leaves an impression in your work. You are also limited to one size and concave shape. If it matches your work. Then great. If not, then you can't change it to match your work.
A little education. The point removed from the above live center on the LEFT has a nice
STRAIGHT side wall that inserts into a STRAIGHT hole. It is not tapered, thus it is easy to make
your own. It is a "Precision Machine Revolving Center". The "Turners Select Revolving Center" is
The point removed from the above Oneway Live Center on the RIGHT has a TAPERED side wall that inserts into a TAPERED hole. It is hard to deal with (to match).
You can use any live center with a removable point that floats your boat. A center with a
straight side wall removable point is a lot easier to deal with.
I like to use the "Precision Machine Revolving Center" or "Turners Select Revolving Center" sold by Craft Supplies USA (The Woodturners Catalog). Both centers are the same size. They both take a 1/2" diameter STRAIGHT side wall removable point.
It is the same center that I use for my "Slip On Custom Centering Cones". See my "Carl's Slip On Custom Centering Cones" blog entry for more info.
You can make the live center points out of any plastic or any hardwood that floats your boat.
Hard Maple is the best hardwood option. Purchase a 5/8" diameter dowel. 1/2" diameter hardwood dowels are often a lot less than a 1/2". Thus, you need to start with a 5/8" hardwood dowel and turn it down to a 1/2" to get a nice snug fit in live center.
UHMW is “ultra-high molecular weight” polyethylene plastic. It is the best plastic option. Hard but not to hard. Easy to turn with a bowl gouge.
UHMW is not as hard as Nylon or Delrin plastic. Not as hard as steel or aluminum. It is like hard maple wood. But, it does not have any end grain wood that can cause problems.
You can purchase UHMW Rods from McMaster or Amazon. You only need a piece of 1/2" diameter UHMW that is 1-1/2" long.
1/2" diameter rods are Mcmaster.com #8701K41. 1 foot of rod is only $2 on 12/12/2023. However, the shipping is going to kill you. Thus using a hardwood dowel may be your best option if you can't find a cheap 1/2" UHMW rod on Amazon.
Note: One foot long rods fit in McMaster's standard 18" shipping box and thus do not incur an extra shipping charge. Longer rods will be shipped in a shipping tube and will cost more to ship. Thus two 1 foot long rods is often cheaper than one 2 foot long rod.
Make Your Own
1/2" diameter UHMW Rods are often a little more than 1/2". Thus you need to turn them down to
1/2" diameter hardwood dowels are often a lot less than a 1/2". Thus, you need to start with a 5/8" hardwood dowel and turn it down to a 1/2" to get a nice snug fit in live center.
Do the following:
- Remove the point from your Live Center. Measure the diameter of the point. It should be 1/2" if you are using a "Precision Machine Revolving Center" or "Turners Select Revolving Center".
- Cut off a 1-1/2" long chunk of 1/2" UHMW Rod or 5/8" hardwood dowel.
- Mount it in a 4 jaw chuck, collet chuck , or Jacobs drill chuck.
- Use a parting tool to turn a 1/2" diameter tenon that is 1/2" long. A tenon that fits snugly in the hole of your live center.
Note: In the photo I am using a Record Power SC2 chuck with "Pin Jaws". It works great on small things. See my "SC1 & SC2 Mini 4 Jaw Scroll Chucks" blog entry.
- Remove the blank from chuck and turn it around. Tighten the chuck down on the tenon you just turned.
- True up the end. i.e. get ready to drill a hole.
Use a spindle gouge to SCRAP a concave shape. See photo.
Make the transition into the hole SOFT, rather than abrupt. i.e. Round over the edge were the concave shape intersects the hole.
You may need to use a 1/4" or smaller spindle gouge or bowl gouge in SCRAPING mode. i.e. a pen turning tool.
The point on the end of the Christmas Tree Ornament in the photo will fit securely in the Hollow Concave Cup Live Center Point.