Help, please: Brite Cutting on Convex Surface

[txtwang]

I have a few questions on brite cutting the overlays on the bands of a set of spurs I made. The convex surface is on a 3" dia. I'm currently practicing on steel pipe to get the "feel" of engraving on a convex surface. I don't seem to have this problem on buckles because the arch is not as severe. I'm sure alot of my problem is inexperience. I am a August grad of GRS school.
I'm using a Gravermach w/ a 901 handpiece. I have my speed set to about 17-1800. I'm normally around 2300. I'm using a 42 flat graver, 40 degree face and 20 degree rounded heel. I am engraving on sterling silver.
1. When engraving on the curve, should I try and keep the engraving surface as upright and centered as possible? Seems sometimes I need to "lean" (spin it on the vice holder) my vice instead of turning? Is this normal?
2. When I do stop to try and keep everything at the top and centered, when I restart, I seem to loose the angle of attack and either dig in or slip completely out of my existing line.
3. Any suggestions or changes to graver face or heel angles?
4. I also have some overlays (yep, on the curve) that I need to use either a square or 120 degree(or something inbetween) graver. I have more problems with these gravers digging in and slipping than with the flats, especially when I have to recenter and restart.
I will continue to cut on the steel pipe until I finally figure this out. If anyone's got any tips that I should try...I'm all ears.

Thanks in Advance
Jerry

 

[griff silver]

just a thought....... try to make your cuts backwards,(from tips to origin) that way youll be cutting down hill and not up hill.
PS. CONTRABAND is great hot sauce but better have some water near by; we all ate brisqute with it sunday for lunch goooood stuffff but spicy!!!

 

[rod]

Jerry,

When bright cutting silver, it gets tricky when you leave the flat earth society and enter warped space! Especially cutting on cylindrical surfaces, it is not easy to get a smooth bright cut with the surface varying under your wide flat.

I would put aside the steel pipe and get some houshold copper plumbing pipe to practice on ... it handles much closer to silver.

I have designed a special holder for wide rings but the diameter is more like one inch.

My suggestion is to practice on tighter curves, like one inch dia or 1.5. Use a length of about six inches, so you can hold onto one end and engrave at the other end.

Find a metal bar that closely fits the inside of your practice copper tube, you can add some masking tape to make up the difference. Put the bar in your ball vise, sticking out horizontally, put the copper onto the bar so that it will revolve, but not loosely. Now you can hold the copper pipe and turn both your vise and the copper with one hand and in one action. Use this for your practice, and when you go to the gentler curves it will be easier.

Do not be ambitious on the width of your wide bright cuts. You need to develop muscle memory that is always aware of the curvature. I suggest a steeper heel that 20 degrees and curved, it will cut slower but not run away. Try to turn your work as you engrave so your tool is always at the top of the hill. Bring your fingers down near to the tool point.

practice

best

Rod

 

[MichaelBaer]

Hello Jerry,when cutting a curved surface imagine that the spot you are at is part of a globe.Think of gravity and how it pulls everything equally towards the center of the earth.
Your downward pressure should always be toward the center of the imaginary globe.
happy cuts, MichaelBaer

 

[txtwang]

Thanka to all the replys and tips. I'm trying to find copper pipe in the dimensions mentioned. 1" sems to be the norm and anything over that is hard to find...especially a smaller piece....I'm still on my steel pipe..I suppose any practice is better than nothing...Thanks again.
Any recommendations on single point graver angles..I've been using a 90 and 120 with 15 degree heels...
Thanks
Jerry

 

[John B.]

Jerry,
If you're working on a tight convex and having problems with your regular gravers here is a little trick you might try.
Try using a graver with much reduced angle of heel or NO heel at all.
Give it a try keeping your angle of attack just past 12 o'clock.
In other words, just slightly up hill.
You might just like it, many find it easier.
Best.