Design Guide for Bonded Plastic Plates
Update/changes: 15 May 2007The following information is intended to provide a general guide for MicroAdvances manufacturing requirements and to help in the understanding of the limitations and capabilities of designing custom fluid circuits and manifolds in plastic. Users should undertake sufficient verification and testing to determine the suitability of this guide's suggestions for their own purpose. This guide is not intended as a warranty or fitness for a particular purpose.
We use one of four types of plastic in our manufacturing of bonded plates. For information on specific mechanical, electric, thermal or chemical resistance properties, click on one of the buttons below.
- All dimensions shown in the illustrations below are in inches.
1. Dimensional limits of bondable plates
Our bondable materials include acrylic (FF & GP), clear PVC, Polysulfone, and
Ultem® (polyetherimide).
min - max (in inches)* Preferred thicknesses
You may combine different plate thicknesses with each other. However it is usually more economical to use the same thickness for all plates if possible.We can bond up to 6 plates together depending on the absolute maximum thickness. If your total design thickness exceeds 1.75", keep in mind that special tooling will be required to bond the plates.
If your dimensional requirements exceed the above limitations, contact MicroAdvances for possible alternative solutions.
- 2. Using opaque plastic
Our standard plates and manifolds are made from clear acrylic or clear PVC. If, however, you must use an opaque color, keep in mind that opaque plastic is slightly more expensive. Moreover, because we need to inspect the integrity of our bonding method, only one layer can be made opaque. If you require opacity, put the opaque plate on the top, bottom, or on one of the middle plates.
Our standard opaque colors are black or white and available only in acrylic. Other colors can be obtained, but only on special order
- 3. Keep machining on top surfaces
Although machining can be done from both sides, it requires flipping the plate which means double the setup time, and can create alignment problems.
Machining from the top surfaces allows for better tolerance control and is less expensive to manufacture.
Always try to design your plate with holes, threads, counterbores, countersinks, grooves, etc. machined from the top surface.
4. Keep machining away from the edges.
Edges of mounting holes or mounting threads should be kept .150 away from plate edges. For other features (such as channels, holes, threads, etc.) keep a min. of .100 away from plates edges.
5. Allow ample distance between features
Allow at least .060 land area between channels and features, and at least .045 between round holes and channels and other features. The more the better.
6. Put radii on channel paths
Designing channels with generous radii allows for shorter CNC tool paths and provides better laminar fluid flow characteristics.
7. Channels (grooves) in plates
Putting round grooves in plates requires flipping the plate for machining which is more expensive to manufacture and can create tolerance and misalignment problems.
Square channels are better but the sharp corners can create stress points.
Square channels with radius corners are better yet but may require special tooling or double machine paths which can be more expensive to manufacture.
"D" channels are generally the best choice for economy and for most fluid functions.
See the chart below for MicroAdvances standard channel dimensions.
8. Channel (groove) dimensions and volumes
X= AREA
(Cubic inch/inch)
µL/inch
1/(µL/inch)* .020 .00035708 5.8513232 .170901515 .027 .00650777 10.6640336 .093773122 .031 .00876133 14.3568521 .069653151 .040 .00142832 23.40529 .042725379 .047 .00196593 32.21499 .031041441 .063 .003487105 57.1418282 .017500315 .078 .0054412 89.1628 .01215439 .094 .0078731 129.0136 .00775112 .125 .0139484 228.5686 .00437505 .187 .0312168 511.5411 .00195488 .250 .0557936 914.2760 .00109376 * Multiply valve by desired volume to get proper groove length.
1µL= .000061025 cubic inches
The chart above shows our standard channel dimensions. The channels are machined by using a ball-end mill. If you wish to modify the channel depth, it is preferred that the depth dimension should not exceed 1.25 times the width dimension.
9. Mounting hole washers
Try to keep washers within the area of the plate. Washers that hang over the edge can create stress on the edges.
10. Mounting hardware methods
Use plastic washers to protect the integrity of the plastic finish. The above methods are examples of preferred ways of using mounting hardware.
11. Using Recessed Screws
Do not use flat head screws in plastic. The stress on the plastic can cause "crazing" or eventual cracking. If you must use recessed screws, consider using counterbored holes with standard head screws and locking hardware with a plastic washer to protect the plastic.
12. Drilled holes, counterbored holes
If you have a choice between using a drilled hole or a counterbore, choose the drilled hole. Drilled holes are more economical and easier to manufacture than bored holes. Keep the depth at least .030 away from the bottom.
13. Threads in plastic
It's always better to put threads through a plate, if possible. Through threads are more economical than blind threads. However in some instances, features in the plate below may interfere with the thread (such as grooves). You may then have to resort to putting in a blind thread. The illustrations above show examples of threads in order of preference (from left to right).Through thread with clearance hole: Best choice if you have the room.
Through thread with no clearance hole below: Make sure your screw length choice allows for at least 4 threads of engagement, or at its maximum tolerance, does not interfere with the plate below.
Blind thread with drill lead: The most used method for blind threads.
Blind thread with counterbore lead: More expensive than drill leads, but allows slightly more fully formed threads.
Thread milling: Allows the most fully formed thread depth, but not available for small threads. Use this for 10-32 threads or larger.
Important: Regardless of which method you use, make sure you allow for at least 4 fully formed threads.
14. Mounting components by using threads in plastic plates
Threads are put in the plate before bonding. Do not try to put matching threads in more than one plate. Instead use one plate for threads. The illustrations above are possible ways to mount components. If your thread size is below 1/8 inch diameter, consider using threaded inserts (see below). However, we can put threads in plastic as small as #0-80 thread size if this is a requirement for your design.Important: Never use liquid thread locking agents such as Loctite®, or sealing pastes. The solvents in these liquids will eventually degrade the plastic and can cause "crazing" or cracking. Instead, use lock washers on the component side.
15. Threaded inserts
All of our threaded inserts are made from nickel plated brass. The following chart shows the dimensions
for our standard insert holes:
INSERT HOLE CHART
(Outside thread)
(Tap Diameter)Z Bore Depth
Style
Insert
Part Number0-80 UNF M2.5 x 0.45 .081 +.002 -.000 .115 ±.003 .190 ±.003
A
C000067 M1.7 x 0.35 5-40 UNC .101 +.002 -.000 .115 ±.003 .190 ±.003
A
C000070 1-72 UNF 5-40 UNC .101 +.002 -.000 .115 ±.003 .190 ±.003
A
C000068 M2. x 0.40 5-40 UNC .101 +.002 -.000 .115 ±.003 .190 ±.003
A
C000071 2-56 UNC 6-40 UNF .220 ±.005 M2.5 x 0.45 8-32 UNC
-- .220 ±.005
--
B
C000072 4-40 UNF 10-32 UNF .159 +.002 -.000 .115 ±.003 .190 ±.003 M3 x 0.50 10-32 UNF
-- .220 ±.005
--
B
C000073 6-32 UNC 12-32 UNF
-- .220 ±.005
--
B
C000069 M4 x 0.70 1/4-20 UNC
-- .220 ±.005
--
B
C000150 M5 x 0.80 1/4-40 UNS
-- .220 ±.005
--
B
C000074
- The insert hole chart above is for MicroAdvances standard inserts. If your design requires a threaded insert that is not listed above, please contact MicroAdvances.
16. Pipe or tapered threads
THREAD 1/8 NPTF ADAPTER 1/4 NPTF ADAPTER A .565 REF .688 REF B .203 REF .250 REF C .25 REF .564 REF D .315 REF .315 REF E .510 REF .510 REF F .215 REF .215 REF G .325 REF .325 REF H .500 REF .500 REF We do not recommend putting tapered taps directly into acrylic (although, in some cases tapered threads can be put in PVC). Instead, consider using press-in fitting adapters. We use either 1/8 NPT or 1/4 NPT fitting adapters. If you require a tapered thread different than this, contact MicroAdvances.
Note that both 1/8 NPT and 1/4 NPT adapters use the same press-in dimensions (D, E, G, H). Plate thickness F is a typical thickness but not a requirement.
Adapter material: brass with nickel plate.
17. Chambers, volume areas
If your design requires an air chamber, or accumulator, and no liquid is going through, consider using simple round holes or slotted holes. If your chamber requires a unique shape, always put radii on the inside corners.
If you require a dispensing chamber or volume containing liquid, consider how the liquid will drain from the chamber. If your chamber requires complete emptying of the liquid, put a 45° angle on the bottom or top outlet surfaces. The illustrations above describe typical ways to achieve this.Volumes with widths up to .375 can be simple slots with the bottom surface angled at 45° (for gravity draining). Volume widths over .375 should intersect smaller slots for draining (this helps break up possible bubble build-ups).
Important: Be careful of the area of your chamber and the pressure you intend to use. The pressure may exceed the stress limits of the plastic and may cause bending for cracking of the plastic. If you need large volumes, consider making them long and narrow, or add ribs for strength, or increase the thickness of the top and bottom plates.
18. Check valves in plates
The illustrations above give the basic dimensions of typical check valve designs. Make sure other internal features (grooves, holes, etc.) do not interfere with the choke features. Keep other features, not related to the check -valve at least .045" away.
The check-valve holder is made from acetal homopolymer (black).
Note, the .20 dimension may vary depending on design requirements.
19. Chokes in plates
The illustrations above give the basic dimension of typical choke-in-plate designs. Make sure other internal features (grooves, holes, etc.) do not interfere with the choke features. Keep other features not related to the choke at least .045" away.The choke holder is made from acetal homopolymer (black).
Note, the chokes are available in a variety of orifice sizes but the housing size remains the same.
20. Pneufit® Tube Cartridge Fittings
Norgren Pneufit® cartridge fittings allow flexible plastic tubes to be easily inserted and removed. The tubing should conform to SAE J844d Type A and B.The brass cartridges are permanently pressed into the plastic plate which hold a snap-in brass flange collar. To insert the tube, simply insert the tube into the collar until it seats at the bottom. The collar grips and holds the tube in place while a Buna-N o-ring seals it. To remove the tube, simply press the collar down and pull the tube out.
We provide for two Pneufit fitting types: one for 1/8" O.D. tubing and one for 1/4" O.D. tubing.
The 1/8 tube Pneufit fitting can be located as close as .56 min. from center to center of each fitting (or .25 from hole edge to hole edge). The 1/4 tube Pneufit fitting can be located as close as .66" min. from center to center of each fitting (or .25 from hole edge to hole edge).
Make sure that no machine features (such as threads, grooves, holes, etc.) come closer than .25 to the hole edges (.307 Dia. holes for 1/8 Pneufit cartridges, .406 Dia. holes for 1/4 Pneufit cartridges).
21. Characters and labels
If you wish to label certain ports or components, we can mill characters into the top plate. The characters are formed by CNC machining with a ball-end mill. The line widths are approximately .020 wide and .006 deep. The characters are typically .114 high, maximum, and .086 wide.It is preferred to mill the characters only on the surface of the top plate. Milling on the bottom would require flipping the plate, thus increasing machine set-up time and cost. If you need characters read from the bottom, we can reverse the characters so that they can be read from the top plate, through the clear acrylic.
Silk screening characters is also an option you may want to consider. Although MicroAdvances does not silk screen in-house, you may wish to second source this operation from a silk screening company in your area.
22. Tolerances
The tolerances below serve as a general guide and represent the limit of our machine capabilities.
All tolerances shown below are in inches.
| Overall plate tolerance (X & Y dimension) | ±.015 |
| Plate layer thickness: (to .38 thick) | ±.005* |
| Total stack-up plate thickness after bonding (up to 4 layers): | ±.020* |
| Drilled hole diameters up to .25 Dia. | ±.002 |
| Drilled hole diameters over .25 Dia. | ±.003 |
| Milled hole diameters (.187 Dia. and over) | ±.001 |
| Drill hole depth | ±.010 |
| Milled hole depth | ±.003 |
| Blind thread depth | ±.020 |
| Channel (groove) width | ±.002 |
| Channel (groove) depth | ±.003 |
| Features: (holes, threads, etc.) to edge of plate | ±.015 |
| Between holes (Position tolerance @ Maximum Material Condition (MMC): |  |
| Concentric features (holes in blind bored holes, etc.) in a single plate. (Position tolerance @ MMC): |  |
| Concentric
and symmetrical features through multiple layers (Position tolerance
@ MMC): |
|
*
If necessary, we can fly-cut plate layer thicknesses to tolerances
of around ±.002. Important: The tolerances above do not take into account the shrinkage/expansion due to the coefficient of linear thermal expansion of plastic. Acrylic, for example, typically has a CLTE of around .000040 in/in -°F. |
 MicroAdvances, Inc. | 6073 N.W. 167 St., Bldg. C-21 | Miami, FL 33015 | Tel: 305-556-4801, Toll Free: 877-62MICRO, Fax: 877-60MICRO |
