Making your own base for photopolymer plates


HOW TO
At the shop we have been going back and forth over whether to use wood backed magnesium (metallic) or photopolymer plates for printing. We have heard a lot of good and bad things about both and many people have told us that its really something you need to try and see. Luckily the company we […]

At the shop we have been going back and forth over whether to use wood backed magnesium (metallic) or photopolymer plates for printing. We have heard a lot of good and bad things about both and many people have told us that its really something you need to try and see.

Luckily the company we use for magnesium plates (Hodgins Engraving), located in Batavia NY, will cut and mount the metal onto wood blocks to make the design type high. However, when using photopolymer plates you will need a base to raise the design to type high. The most popular base currently on the market in my opinion is the Boxcar base from Boxcar Press. Standard bases from Boxcar start at $150 for a 4.5″ x 7″ base all the way up to $1150 for a 24″ x 24″ base. They also sell deep relief bases for use in conjuction with their deep relief photopolymer plates on platten presses.

The question is: Is it possible to make your own base?

The simple answer is yes as long as you have access to micrometers, an end mill, and of course a milling machine. You will also need a piece of Aluminum larger than the base you want to make. Aluminum is chosen because it is easy to machine yet hard enough to provide a good impression. McMaster-Carr sells a wide variety of metal stock in almost any size you will need. If you have a local machine shop you might be able to purchase directly from them and save on the shipping. Sometimes you might even be able to get a scrap piece for cheap or even free.

The press we are going to use to print the photopolymer plates is our beloved new style C&P Pilot (6.5″ x 10″). The inside of the chase measures roughly 6.5″ x 10″ however you will need to leave space on each side of the base for furniture and quoins to lock it up. Many printers will suggest that you leave 0.5″ of space on each side of the base both for lock up as well as guage pins. We settled on a base size of 6.25″ x 9.5″ since we wanted to maximize our printable area but still leave sufficient room for lockup.

The last dimension you have to determine is the thickness of the base which is determined by the specific thickness of the polymer plate you will use. In order to print the photopolymer, it must be mounted type high, which in the U.S. is 0.918″. If you plan to use photopolymer plates made by Boxcar Press or another manufacturer who supplies similar plates, then you have some choices:

Mfg.
model

surface

hardness

face
relief


thickness

Class

Jet
94FL
matte
62
.027″
.037″
A
Jet
94CH
smooth
75
.027″
.037″
A
BASF
WFH IV 95
matte
65
.026″
.037″
B
KF
152*
matte
65
.045″
.060″
B

(Source: Boxcar Press)

The top model Jet 94FL is the most common plate used with a standard base. There are also the Jet 94CH and WFH IV95 which provide varying face relief and hardness depending on your preference and setup. Note that the thickness of the top three plates are the same so they can be used interchangeably on the same base.

The KF 152 plate was designed for use as a deep relief plate and therefore is made from a thicker polymer. Since the polymer in this plate is almost twice the thickness of the other models, you will need a different base thickness. The benefit of this model is that the face relief is .045″ which is almost .02″ deeper to minimize inking of the base and plate backing by the rollers on platen presses.

We chose to use the standard Jet94FL plates for our C&P Pilot and therefore we made a base that was .875″ thick (.918″ – .037″ = .881″). We chose a thickness of 7/8″ (.875″) instead of the .881″ for two reasons: the standard base sold by Boxcar is 7/8″ thick and 7/8″ is stocked by most machine shop. Stock of 7/8″ aluminum plate is machined to 7/8″ with a uniformity of .001″ or better. If you can’t get 7/8″ aluminum plate you can always use 1″ thick aluminum plate and mill the thickness down to 7/8″. It is important that your base has a uniform thickness otherwise you will get different impressions in different regions of your base. Which can be a headache when trying to make quality prints.

So now that we have the dimensions of our base, 6.25″ x 9.5″ x 7/8″ (L x W x H), we can machine it. The machining process is relatively simple, first you need to square the edges of the aluminum since it was most likely cut for you out of a larger piece using a band saw which leaves a jagged edge. Hopefully you should have at least one flat side which you can use to set the piece up in the mill either in a vice or using clamps. You should mill the part on each of the parallel sides using your end mill cutter (I used a 5/8″ end mill) to the desired dimension, in my case it was 9.5″. Now two sides of your base are flat and parallel.

Next, rotate the piece and using a T-square lock up the base on the bed with clamps. To insure that the piece is square in the mill, run a dial test indicator along the flat side of the base. Adjust the clamps until the indicator gives a variation to your liking (a few thousandths of an inch variation was sufficient for our base). Now that the piece is square you can mill these sides to the desired dimension (in our case it was 6.25″).

Lastly, remove any sharp edges or burrs from the base using a file being careful not to scratch the base. Here are some pictures of what our base looked like when it was all finished.

Top view of the finished base locked in the chase

Close up side view of the base locked in the chase

Base locked up and ready to print

If you have any questions about making your own base feel free to call or email us, we’d be happy to explain it further.

23 thoughts on “Making your own base for photopolymer plates


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