• Bolt circle diameter: 4.25"
• Adapter boss diameter: 2.26"
• Adapter boss height: 0.53"
• 3 Mounting holes is already drill and tapped on the back plate to match the 5" ER40 zero set adjustment collet chuck.  A light skim cut is required on the adapter boss OD and the face of the adapter's contact area.  The clearance between adapter boss OD and the chuck counterbore ID should be from 0.0078" to 0.0129".  The adapter boss nose should not be in contact with the bottom of the chuck counterbore.  The gap between the adapter boss and the bottom of the counterbore should be around 0.0787". 

How to process back plate to guarantee ER40 Collet Chuck's T.I.R?

Back plate can be mounted onto ER40 Collet Chuck. As long as back plate Shoulder Diameter D1=3.78" > ER40 Collet Chuck's D1=3.74" , all ER40 Collet Chuck will fit in. All back plates have 0.04" allowance, please measure the size of Chuck's D1 before process your back plates. The size of back plates's D1 should be a little bit smaller than the size of Chuck's D1. Because the gap between back plate and chuck is smaller, chuck's TIR is better. No gap is the best. Note, for fully-machined back plate, D1 need to be processed before they can be mounted.

You would not need to drill any mounting holes but you will need to turn the shoulder down .040" to match the back of the lathe chuck to make the chuck & back plate more concentric with the lathe spindle. When turning the shoulder of the backing plate, ONLY TURN THE SHOULDER OF THE BACKING PLATE WHEN ATTACHED TO THE LATHE SPINDLE. If you use a chuck to clamp the backing plate and then turn it, the backing plate will not be true to the lathe spindle and will have more runout than specified when the chuck and back plate are put together. 

How to minimize Chuck's TIR?

1. Before you buy the chuck please check your spindle's runout.

Related products 5” ER40 "SET TRU" Collet Chuck W/Fine Adjustment +1-3/4-8 Back Plate p/n: 202-1029+1538+6175  5” ER40 "SET TRU" Collet Chuck W/Fine Adjustment +1-10 Back Plate p/n: 202-1029+1538+7044  5” ER40 "SET TRU" Collet Chuck W/Fine Adjustment + 2-1/4-8 Back Plate p/n: 202-1029+1538+7045

Related products 5” ER40 "SET TRU" Collet Chuck W/Fine Adjustment +1-1/2-8 Back Plate p/n: 202-1029+1538+7046  5” ER40 "SET TRU" Collet Chuck W/Fine Adjustment +D1-3 Back Plate p/n: 202-1029+1538+7047 5” ER40 "SET TRU" Collet Chuck W/Fine Adjustment +D1-4 Back Plate p/n: 202-1029+1538+7048

Related products ER40 Collet Wrench p/n: 202-1538 ER40 Collet E Wrench p/n: 202-1392 Optional Accessories 12PCS ER40 Collet Set p/n: 202-6494

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If the item stated as brand new is found defective on arrival or incorrect item was shipped, buyer understands that the product will be repaired or replaced at seller's discretion, and be given a reasonable amount of time. Buyer is responsible for return shipping costs and insurance. Warranties are offered by the manufacturer and will be honored by the manufacturer. All shipping and handling fees will not be returned in any case.