Machining Gland Covers

[jmshep]

Can any one recommend a method for machining the profile of gland covers etc similar in shape to the attached picture. I struggle to get them symmetrical, particularly the smaller ones.
I have tried milling the straight edges to scribed lines and finishing off with a file but I don't find it easy to set up each face with repeatable accuracy and I can't visualise a jig that will help.

Will be grateful for any suggestions (preferably ones not relying too much on a hacksaw and file!)

John

 

[Noitoen]

You could make a pattern out of some "harden able" steel, with a hole to bolt on to the brass part and then use it to file down the excess brass. The file won't go past the template.

 

[jmshep]

Thanks but how do I machine an accurate template? If I was doing a production run that would be OK but I only need to produce one offs.

 

[tel]

Just use three filing buttons once you have turned the spigot and drilled the holes. the two outer ones (obviously) the size of the outer radii and the inner one to the middle radius. You have to be a little bit creative with the lengths of the buttons so the while shebang can be grabbed in thew vise.

 

[kvom]

I would do it as follows:

1) True up an oblong block to the outer dimensions, then drill the holes.

2) With an angle block at the desired angle (looks like about 15 degrees) clamp the block in the vise and mill one of the 4 sides to the approximate depth needed. You can go part way and then reverse to cut the opposite side to check. As long as you don't change your parallels or the spindle height everything will be symmetric. When you have one end done, then you can set the milled face on the parallels and mill the other end, which are parallel to the angles you just made. Once again, using the same spindle height you'll get the same dimensions.

3) Make a mandrel and drill/tap matching holes. Screw your part to the mandrel and mount the mandrel in a 4-jaw chuck so that the piece is centered on the lathe. Turn the spigot and drill as needed.

5) Rounding the ends would be done filing, sanding, or using a rounding table as available.

 

[bearcar1]

Have a look at reply #33 here. It will give you a visual idea of the method that Tel is speaking of. I used it to good advantage in that build.

www.homemodelenginemachinist.com/index.php?topic=4758.30

BC1
Jim

 

[jmshep]

Thanks for the replies - The filing buttons are certainly the way to go.

I also found a tip using dills to position the gland in the milling vise to get each of the four faces symmetrical in this excellent site:
http://start-model-engineering.co.uk/tag/stan-bray/
(photo about halfway down the page)

Using that method for a start and finishing off with the filing buttons has given me a profile for this type of gland that I am happy with at last.

John

 

[tel]

Glad you got there John. Those glands were a real puzzle to me in the early days as well.

Couple the buttons up with this handy little turning fixture (shown here doing crank arms, but the principle is the same) and the job becomes a piece of cake.

 

[RobWilson]

Hi may be Like this , make up a small fixture for the lathe and turn them

Cheers Rob

 

[Kermit]

Rob. That is a brilliant, simple prodedure.

Thanks, it's MY method now. :big: (for when I get to that step in my journey)

imitation is the sincerest form of flattery,
Kermit

 

[shred]

Another way if you wanted the angled-corners in the middle is to pop a drill or bit of rod through one end hole, another through the center hole (probably about the same size as the rod in the first hole) and use the shanks to support the part on your vise jaws. Repeat for each flat. Round the ends with buttons or the other rounding jigs.

Here's one making a flat parallel to two holes. With different sized holes or rods you get angles.

 

[Tin Falcon]

rob I like that !! this question my a be a bit silly or lazy but how do calculate or find the hold down locations.
Tin

 

[kvom]

rob I like that !! this question my a be a bit silly or lazy but how do calculate or find the hold down locations.
Tin

Since Rob hasn't stopped back, I'll take a shot at this. There are lots of "solutions" depending on how you want the profile to look. It's easier to sketch in a CAD program to decide on the dimensions, but lacking this you can do the following calculations (Excel will be useful to play around with fitting the figures).

First set R1 is radius of mounting holes and R2 is radius of center hole, with D1 being the distance between the hole centers. Then assume R3 is distance from the centerline of the lathe to the center of the mounting hole. You can then calculate the distance between the center of the lathe to the center hole via the pythagorean theorem R4 = sqrt(R3^2 - D1^2).

Finally choose a thickness T1 of material you want between the edge of the mounting hole and the final profile. The radius of the outer cut will be R5 = R3 + R1 + T1. The thickness of the material around the center hole will thus be R5-R4-R2.

If all the numbers seem to work, you need some stock that is at least R3+R1 plus enough extra to drill the holes for the screws. Both mounting holes need to be the same distance from the center (i.e., R3). Rob's drawing shows the material as R5, but it can be smaller as long as the mounting screws fit.