General Fixture Plate FAQ

What are the benefits to using a modular fixture plate on a CNC machine?

• Increasing the workholding, clamping and setup area
• Convenience of having hundreds of bored and tapped holes versus a few t-slots
• Indexing, shifting, locating and holding large parts
• Clamping large parts outside of the machining envelope
• Using the SMW Mod Vise low profile, modular work holding system!
• Protecting the CNC machine table (often made from soft cast iron)
• Quickly aligning, tramming, and clamping vises and other workholding
• Using custom, hot-swappable fixture plates tops

Should I buy an aluminum or steel fixture plate?

• Steel plate benefits: machined from 4140 alloy steel, these are our premier line of fixture plates. The high quality, hardened (26-30 HRC) alloy steel means these fixture plates are the strongest and toughest, well suited for daily use.
• Aluminum plate benefits: lower price and lighter weight means reduced shipping cost and easier installation.
•  7075 Anodized Aluminum fixture plates are an excellent mix of value, weight, and strength. 7075 aluminum has nearly twice the tensile strength as 6061. The anodized surface increases wear resistance, helps reduce scratches, and offers galvanic corrosion resistance. Threaded holes are form tapped for maximum strength.
• 6061 Aluminum fixture plates are our value line offering. We take pride in the manufacturing process and tolerances of these plates and they are a great way to increase the workholding envelope, implement the SMW mod vise system, and minimize setup time on your CNC machine! Threaded holes are form tapped for maximum strength. NOTE: when these plates are installed on a non-aluminum surface such as a bare machine table these plates must be used with a galvanic corrosion inhibitor (e.g. dielectric spark plug grease) and be removed frequently to inspect for condition and/or re-apply the corrosion inhibitor. Corrosion inhibitor is available for purchase here.

What is the hole spacing on SMW fixture plates?

• Standard 1/2" SMW Fixture Plates have a hole spacing of 1.250" on-center. These plates have our double offset pattern (an additional hole pattern on the same spacing occurs between the first pattern, giving you more fixturing holes).
• 1/4" SMW Fixture Plates have a hole spacing of 0.750" on-center. Not all 1/4" plates have our double offset pattern.
• M6 SMW Fixture Plates have a hole spacing of 20mm on-center. Not all M6 plates have our double offset pattern.

Is each hole bored and threaded?

• On standard 1/2" SMW Fixture Plates each hole is precision bored 0.25" deep for use with a 1/2" dowel pin, the SMW Mod Vise or other 1/2" accessories. Below the precision 1/2" bore each hole is tapped 1/2"-13 UNC.
• On standard 1/4" SMW Fixture Plates each hole is tapped 1/4"-20 UNC. Most plates do not have bores, instead we recommend our 1/4" Fixturing Pin.
• On standard M6 SMW Fixture Plates each hole is tapped M6x1.00. Most plates do not have bores.

What is the appropriate torque spec for my fixture plate?

• When installing your plate we recommend 60 ft-lb (81 N-m) for the low-profile SHCS that secure the fixture plate to the T-Nuts. NOTE: This value is only for our standard 1/2-13 UNC low-profile SHCS which are common on most Tormach and Haas fixture plates. Please verify the maximum acceptable torque for bolts and mounting hardware of other sizes.
• When using the plate the appropriate torque for workholding depends on a variety of factors, including the thread engagement of the stud or screw into the fixture plate. 
• For the 1/2"-13 holes in aluminum plates, we recommend up to 45 ft-lb or 61 N-m.  DO NOT exceed 50 ft-lb or 68 N-m. 
• For the 1/2"-13 holes in steel plates, we recommend up to 50 ft-lb or 68 N-m. Do not exceed 70 ft-lb (94 N-m). 
• For 1/4-20 holes in aluminum plates, we recommend 75 in-lbs (do not exceed 110 in-lbs)
• For M6 holes in aluminum plates, we recommend 69 in-lbs (do not exceed 100 in-lbs)

Why does my aluminum fixture plate have set screws in the back?

• These holes are used for fixturing during the anodizing process.

Are solid models provided?

• Yes, solid models and product drawings are available for download on their respective product pages.

Will you machine a custom plate for my machine?

• Yes, please contact us via this form.

How do I set up and install my SMW Fixture Plate?

• Click here to watch our instructional video

How do I prevent rust on my steel fixture plate?

• Click here to read our article on machine shop rust prevention
• We recommend LPS-3 or lanolin as a rust preventative for our plates

What maintenance do I need to do on my fixture plate?

• We recommend any workholding device (fixture plate, vice, 4th axis, etc.) be periodically removed and cleaned.  This interval depends on personal preference, frequency of use, types of material being cut, coolant and more but generally should be inspected every 3-12 months.  See FAQ item above for tips on preventing rust.

What is the lead time on fixture plates? Are they kept in stock?

• Most products are kept in stock and ship within one business day.
• Out-of-stock fixture plates typically have a 7-10 business day lead time (plus an additional 2-3 weeks for anodized plates).
• Please contact us to confirm inventory and lead time for urgent orders.

What are the plates listed as "Used"?

• Occasionally (albeit infrequently) "used" plates will be added to the store at a slight discount. These plates are still functional but have been previously installed (typically used in the SMW shop) and may have slight cosmetic defects. Specifics will be noted on the product page, contact us for questions about a specific plate.
• Orders on used or blem fixture plates are final, non-canellable, and non-returnable.

Tolerances

What is the flatness tolerance of an SMW Fixture Plate?

• We do not qualify plates in an unconstrained state. However, we do evaluate and process the raw material in a specific way so that when the fixture plate is secured to the machine table, it's "flatness" will be the result of the parallelism tolerance plus any deviation, level, or tram error in the machine table.

What is the parallelism tolerance of an SMW Fixture Plate?

• 1/2" SMW Fixture Plates are held to parallelism of 0.0005" per 18" of plate length (+/- 0.00025") across a single plate.

What is the tolerance between plates for a matched plate set?

• For sets of 2 plates, the parallelism tolerance of the set is identical to that of a single plate (0.0005" per 18"). 
• For matched sets of 3+ plates, thickness at the plate seams is matched within 0.0005". Each plate is then individually subject to the standard parallelism tolerance (i.e. each plate in the set will be parallel within 0.0005" per 18" of length and have a thickness variation of no more than 0.0005" at the edges where plates meet).
• The continuity of the fixturing hole pattern across multiple plates is dependent on careful setup of the plates. These sets have a small gap (<0.005") designed between fixture plates, allowing for some adjustment of the hole pattern alignment. We recommend using our Fixture Plate Set Alignment Jig for installation of these fixture plate sets.

What is the thickness tolerance of an SMW Fixture Plate?

• We prioritize parallelism over the final thickness of the fixture plate. Thickness may vary +0.01" [0.25mm] -0.04" [1.02mm] from the nominal value given. This does not mean the plate will have 0.02" variation in the thickness.
• For example, the measured thickness of our standard 0.950" nominal plates may come out at 0.930". Each point measured along the plate will be within +/- 0.00025" of this 0.930" dimension (the parallelism tolerance).

What is the bore tolerance of an SMW Fixture Plate?

• The 1/2" precision bores on the SMW fixture plates are machined to 0.5005" +/- 0.0002".  We have found this to be the ideal tolerance when using a mix of dowel pins, gauge pins and accessories like the SMW Mod Vise.  Keep in mind, for a dowel pin to have a "slip" fit (e.g. not require hand tools, vice grips, etc. to remove), there must be some gap or "slop" in the fit between the pin and the hole.  

What if a dowel pin has a loose fit?

• Dowel pins can be purchased with varying degrees of tolerance and fit, but traditional "off the shelf" dowel pins (e.g. this 1/2" dowel pin from McMaster Carr) have dimensional tolerance of 1/2" +0.0001 to +0.0003.  A pin cannot fit in a hole of the same size; the hole must be larger.  Our hole tolerance, as described above, allows for this fit.   However, adding a relatively small amount to a bore diameter - even 0.0001" results in a notable difference in the feel and fit of how a pin fits into a hole.  We use a combination of metrology tools, including bore gages and deltronics gage pins, to ensure bores meet our tolerances.