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 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.

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  • http://cathyschofieldkr95.wordpress.com/2008/03/15/corsi-di-aggiornamento-educatori/ Oswaldww

    thats for sure, man

  • http://www.bluestonefolkschool.org Geoff Davis

    I’ve a machinist friend that’s itching to do a favor for the Folk School. I’ll be emailing him about a photopolymer base tonight!

  • Pleadiaallest

    Hi

    As a fresh dolcepress.com user i only wanted to say hello to everyone else who uses this forum :-)

  • http://www.missclinepress.com Ana Karina Luna

    Hello, I have somebody that can possibly make a base for me (happy to find your post!). But in my case I will be using deep relief plates. So, 0.918 – 0.06 = 0.858″. Should I round this number too like you did yours? Do you know how thick is the deep relief base at Box Car?

    Also, I’ve been thinking about making it 4.5 x 7.5, in case I want to print metal type with it too. I use photo polymer plates only for small stuff, bigger drawings I usually carve them myself because I enjoy it. What’s your suggestion on this?

    Thanks,
    Karina.

  • http://www.dolcepress.com Alexandra

    Hi Ana,

    We’re glad you found the post helpful. In your case with a deep relief base and plates you are correct that you will want to have the base machined to a thickness of about 0.858″.

    If you are only going to be printing with the base then it doesn’t matter if your base + plate are exactly type high since you can adjust the inking with tape on your rails and impression with packing. If your lucky you have a craftsman or windmill and have adjustable rails. If you are going to be printing other things on the press such as hand set type or cuts mounted on wood then the thickness will be more of a concern.

    Make sure to ask whoever is making the base for you, what the tolerance of the thickness is? Also, the official base that Boxcar sells is anodized with a grid which serves two purposes. First, the grid helps with alignment of plates and second the anodizing produces a slightly rough (pebble) finish which helps to pull plates off. With our original base the smooth mirror finish made the plates stick extremely well, and were therefore very hard to remove.

    As far as choosing a size for the base you will want to pick something that doesn’t fill up the entire chase so that you have room for gauge pins. You can also consider cutting a larger base into a few pieces and only use a small piece when you have small plates. But if you need more space you can lock up several pieces in one chase.

    I hope that answers your questions,
    Alex

  • http://www.missclinepress.com Ana Karina Luna

    Alex, I appreciate the extra info.
    Cheers,
    Ana Karina.

  • http://www.theorientunicornn.in Mouli

    Sir,
    i would like to know a few things about polymer plate printing.
    1. Will cleaning with water on the plate affect the polymer coating? Is it advisable? (magic ink usage)
    2. Or should we use Butanol for cleaning the plates?
    3. Whats the ink density to be maintained?

    We are new to this. Kindly help us out.

  • Brandon

    I have a plate for my kelsey 3 x 5 press, that is 1.5 x 3.5 x .875 (7/8″), and a little confused as to what thickness I should be milling it down to take standard boxcar photopolymer plates. .881? Or do I just leave it at 7/8″ thick?

  • http://www.dolcepress.com Alexandra

    Hi Brandon,

    Standard Boxcar plates are 0.037″ thick and if the base you have is 7/8″ (.875″) thick then the height does not need to be milled down any further. In the end you want your base+plate to measure type high (0.918″) however 7/8″ thick aluminum is a standard stock part and is only 0.006″ lower than type high.

    On most platen presses, especially tabletop and small floor models you will need to put tape on the rails to bring the rollers to the proper height to ink the plate. Therefore, you can just add slightly less tape on the rails. Especially with a Kelsey 3×5, the height of the base+plate is not critical.

    If you have any other questions, feel free to post them.

    Evan
    Dolce Press Staff

  • bill moseley

    We have an old ‘Gordon’s improved platen’ press, which has no chase. We want to get the machine going, using photopolymer plates. We will have to have a chase and base machined up. The aperture for the chase is app. 15inch x 11inch, what would size should we make the inside of the chase?
    Bill

  • http://www.evanmade.com Evan MacDonald

    I’m new to this and have some questions.

    I understand that working with wooden bases for polymer plates is a pain. As I’m looking to make my own base, I’m wondering about the possibility of using a base that’s surface is aluminum (lets say 1/2″ thick) and then below that is some high density wood (aprx 3/8″).

    The reason I ask is because my printable area is 30×45″ (showcard press like the one here: http://itsfancy.com/showcard/Site/Library%202.html) and aluminum at that size is tough to come by much less, expensive!

    what do you think?

    • http://www.dolcepress.com Dolce Press Staff

      Are you planning on printing stuff the full size of your printable area? If not I might start out with a smaller base. Assuming you get a precision milled/or ground piece of aluminum you can lock up multiple pieces together.

      In principle your idea would work. The idea is to get the base+plate to type high (0.918) or higher if your press was designed to work with a galley tray. You can find aluminum in 30×45″ at supply houses like McMaster-Carr but you are right that it will be expensive. If it was up to me I’d much rather sacrifice base size for one solid piece of 7/8″ aluminum.

      Good luck and let us know how it works out!

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  • Chuck-o

    The image links are broken on this page, could you please fix so I can learn this??

    • http://www.dolcepress.com Dolce Letterpress & Design

      Hi Chuck-o,

      Sorry about that, the images should be correct now.

      Best, Evan

  • Megs

    So I’m relatively new to letterpress and I’m taking on a very important project, my best friends wedding invitations.
    I don’t have access to a milling machine and the machine shops in my area aren’t really getting back to me about my project.

    Could I theoretically use the McMaster Carr M1C6 aluminum stock in 6×12, which comes pre-ground to within .005 tolerance thickness and within 1/16″ for width and length if I don’t need to cut it down to fit my (Vandercook) bed? Would it provide a good impression within this tolerance or should I be worried that it might come too thick for type high?

    I know you had mentioned on Briar Press that the anodized coating was critical for you to make plate removal easier but was it really THAT hard?

    Basically I’m cheap and kind of lazy and want to know if I can use the McMaster Carr stock off the shelf, no machining, with relatively good results.

    Opinions?