The topic of how high an altar should be does not appear to have been covered.
Novus Ordo altars are generally lower than traditional altars. There is a
reason for that. When they first started turning altars around in the
1960's (of course, Luther was 450 years ahead of this), they found that
the "thing" was obtrusively high. And it made shorter priests feel even
shorter when they had to look out over the top of a high altar at the
madding crowd.
So they got out the saws and cut them down shorter.
I know one priest who is only about 4'-10" and he has a bit of a problem
reaching into the tabernacle, but he makes it, somehow. He has no
difficulty with the height of high altars that are 50" off the floor, as far as
the vessels and the prayer cards and missal and such.
The problem comes into play for tall priests or priests with back trouble.
The higher altars are easier on them, especially their backs.
So if you are setting up an altar for a visiting priest, keep in mind that you
ought to keep it a lot higher than usual. It's actually at bar height and
above, which is 43" and up. That means at least 10" higher than standard
table top height, which means 27" for folding tables, dining room tables
and conference tables. Hotels use the same tables for conferences as
they do for dining.
A standard desk height is 31" and a standard typing keyboard (old days
the typewriter set on it) is 25" - the pullout shelves in desks are that high
usually.
So obviously, you are not going to have a ready-made piece of furniture
setting around that is the proper height for a real altar.
What can you do in a hurry to put something together?
It shouldn't be the priest's job to find all the parts to construct an altar,
but unfortunately, sometimes that happens. You can elevate a portable
folding table all right, but be careful to make it stable. You do not want the
altar falling over during Mass. The best way to make an elevating device
stable is to make it one piece, that is, no moving parts.
For example, to elevate a table with 4 legs, up 12", you could make use of
a full or part sheet of 1/4" plywood and a leftover fence post 4x4, some
glue and some nails.
You can use the 1/4" plwd for the sides, and short blocks of the 4x4 for
inside the 4 corners. That's what can hold up the table legs, with 3-1/2"
square ends of the 4x4s. The posts can act as glue blocks as well as
stiffeners. Keep the plywood taller on top than the 4x4s by about an
inch or two (more if you're going to add a lid set into the top), and the
table legs won't slip off the platform. Put the whole thing on carpet or a
rubber mat, and the altar will be fairly stable. You can make it a lot more
stable by adding a top and a bottom to the platform. But a single sheet of
3/4" plywood on the top (let the 1/4" plwd go on past the top by an inch or
so) will make your platform almost as stable as the floor.
The idea is to have 4 sides of lightweight plywood making a box around
the legs of your table. Glue and nail the 4x4 blocks inside the 4 corners
of the box, such that the top end of each block is at the same height off
the floor, in this case we said 12" but if you're adding a lid of 3/4" ply, that
would then be 12-3/4" height. The nice thing about 3/4" ply is it's so easy
to nail into, and some glue between its edge and the 1/4" ply face will
make a strong joint.
If you want more detail:
Measure the distance from the outside of the table feet (be sure to
pull/wiggle them out a little so you know they're at rest and at full width),
and write that down. Call it "Leg distance - length (or breadth)." Then
measure the distance from front to back "out to out" and write that down,
calling it "Leg distance - depth".
Cut a 4 x 8 sheet of 1/4 plywood (Or a portion of a full sheet) into 2 or 3
strips just shy of 16" wide each (probably about 15-3/4") and 8' long. The
length needs to be enough to reach past the far side of each leg in front.
Next, take the Leg distance length and ADD ONE INCH to it. Do not forget
to add an inch. That gives you your plywood length. Cut two of the 16"
plywood strips to that length. For example, if your table legs are 59" from
the outside, then your plywood should be 60" long.
Next, take the Leg distance depth and add a half inch. Do not forget to
add the half inch. Cut two more pieces of plwd that length.
The last thing to cut is the 4x4. If you want 12" elevation, and you are
going to use plwd for a lid, cut the 4x4s 11-3/4" long. Then take the
short ends of plwd and glue and nail the 4x4s to the ends of the plwd,
making the sides of the 4x4s flush with the short ends of the plwd., and
flush on the bottom too. The top is where the extra ply hangs over the
end of the 4x4. You'll have two of those when you're done with this step.
Finally, glue and nail the front first, and then the back ply to these two
end pieces. The only trick will be the last side you nail on. If you have a
leftover piece of 4x4, or a 2x4 lying around that's long enough to reach
between the front and rear posts, you can stick that between them to
act as a brace while nailing on the back side.
If you're putting a lid on it, that goes on last. Cut the lid to fit the inside
of the box and nail it in. If the lid is 1/4 ply, you may want to nail on some
glue blocks or strips to the lid first, because once it's attached, it's a lot
harder to nail plywood with no backing. Of course, if you have a nail gun
like a brad nailer, you won't have any problem with that.
When you're done, the platform will be just right to set the table on it,
and provide a stable base for the altar. And when it's not being used
for Mass, the platform can be a storage box for toys or firewood or
whatever. If you want it more durable, thicker plywood may be necessary.
But you can stiffen the bottom edge of 1/4 ply with 1x2s glued and nailed
on.
If all that is too much trouble for you, it's possible to put some cardboard
boxes on top of your folding table, and put a piece of plywood on top of
that. You could use a cutoff door or some other flat material, such as
drywall (2 pieces of 5/8" drywall or sheetrock would be okay) or plastic
(e.g. plexiglass or ABS or fiberglass). If you have a second folding table
that's the same size, that would work: just keep the legs folded up
and set it on top of the boxes. The boxes should be the same height,
in this case 11 or 12 inches. Then you may like to use some duct tape
to secure the boxes to the lower table and also to the top table top.
The reason you want it stable is, when the priest is doing the
consecration or when he's genuflecting, he touches the altar and uses
it for stability. If he has some kind of pain, or if he feels dizzy, he may
lean on the altar. But at the words of consecration, he pushes his
forearms down onto the front edge of the altar and at that moment, he
likely prefers to be thinking about the prayers and not about whether
the altar is going to start moving under his arms. The altar is something
the priest should have confidence in. There are already too many
unknowns without having to worry about this too.
Every traditional priest carries an altar stone to say mass on, and it is
much preferred if this can be set into a pocket on the top of the altar,
and that is 7" square and 11/16" deep. The stone itself is 5/8" thick, and
you don't want it sticking out on top. If it's a little under flush, that's okay,
because you can easily put a few sheets of paper or a napkin under it
to raise it up. The altar stone is where the priest sets the host first, and
then the chalice, during the consecration. It is the first thing that any
priest should have to say Mass. He is obligated to use one if at all
possible. Curiously, most Novus Ordo altars do not provide any place for
one, nor do Novus Ordo priests use one. If you go to old cemeteries,
you will find outdoor altars, ALL of which have niches or pockets cut into
the surface of the altar top, right in front, where the priest places the
chalice during the consecration. I went to the grotto at Ariesville NY and
there, amidst the pine trees and bramble bushes, were several altars
with pockets for altar stones in the top. They were all full of fallen leaves
and compost, for not having been cleaned out for perhaps years, but
they were there, nonetheless, waiting for the next proper priest who
has come prepared with an altar stone.
The top surface of your home altar should have such a cut-out in it, so
that the priest can place his altar stone there. You can have a sheet of
3/4 ply or at least 11/16 (a lot of so-called 3/4 ply is actually 11/16
anyway) on the top surface of your home altar, with a 7x7 cut out. But
one problem is, the plywood tends to be curved. And when it's not flat,
it makes a bulge in the top of the altar, which wobbles up and down
when the priest is trying to pray. No Good.
One way of solving this problem is to "score" the back of the plywood
with numerous deep cuts, about 3/4 the thickness of the plywood. So
for a 3/4 sheet, that would be about 9/16" deep score lines. They can be
made with a handheld circular saw, or a table saw, but the table saw is
a lot of work, unless you have a finish apparatus with a sliding table.
A simpler approach is just get a high grade of plywood, (expensive) or
else use MDF (medium density fiberboard), which is naturally very flat.
It's also heavy. You could use particle board as well, but it tends to have
a smell that is not so peasant. It contains formaldehyde, usually.
The various types of plastic that I mentioned above all would do fine
with an altar stone cut-out. I suppose you could even use a very dense
foam rubber mat, but be sure it is very dense. That actually might be the
most comfortable surface for a priest to use. I've never asked about
that. Someone here may know though..................