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Drill Arbor - MT3 - JT33: Cost $0.50

I had to find a chuck for the mill-drill & the cheapest source was an old broken GMC drill press I had laying around.  Unfortunately the chuck uses a Jacobs #33 taper.  This is unusual size for a Morse #3 taper arbor & I found it hard to get one in my area, so I made my own.  I also decided not to put a tang on the end, but instead secure it with a 3/8" drawbar if required.

Addendum: I have since used the same method to make a milling cutter holder for my 3/4" end mill.  It is almost the same, but was made out of 30mm round stock.  The end opposite the MT has a hole bored in it to hold the cutter, which is then locked into place with a grub screw.  Later I plan to make my own 1" stub arbor & 1" Side & face mill arbor.

Table of Jacobs & Morse tapers in Imperial & Metric are at the bottom of this page.

The MS blank.

1) Check alignment of lathe (headstock, tailstock & centres).
2) Mild steel bar 5-1/2" x 1", Face off each end.
3) Centre drill both ends.
4) Mount between centres, driven by a dog & faceplate.
5) Turn down to a touch larger than 0.938" for about 4-3/4" - becomes the parallel reference surface.
6) Turn down to a touch larger than 0.624" for about 1-3/4"
7) Turn down to 3/8" dia for 1/2"
8) Using dial gauge set offset for turning the Jacobs #33 taper (see table for 1/2 taper "/" below)
9) Engage saddle half nuts, use rotation of leadscrew to get distance along job - 16 turns of 8tpi leadscrew = 2" & I then doubled the 1/2 taper "/" measurement.
10) Take dial gauge reading at each end of 16 leadscrew turns & adjust tailstock offset until required taper is achieved (JT33=0.0635" over 2")
11) Turn taper to the required length (JT33=1")
12) Using Prussian blue, check the taper in the chuck for fit, re-do taper angle if required
13) Polish with fine emery paper

The finished MT3 to JT33 arbor.

14) Flip end for end & swap lathe dog to opposite end
15) Repeat steps 8 to 13, but this time for the Morse taper. (MT3=0.05020 over 2" for the required length (MT3=3.188")
16) Cut arbor to length, face off, chamfer any sharp edges, polish
17) Step drill the hole in the Morse end & tap the thread to match the drawbar.

I found that by using this method, I'm able to make a usable arbor which holds itself in place very well, first time, every time.  In fact, when I push the chuck & the arbor together, I have difficulty getting them apart again without using brute force.

The only difference I would make next time is to allow more length of taper on the arbor, as the clearance between the chuck & the quill is a bit smaller than I like.  The easiest way for me to do this in future is; probably extend the MT3 tapered section's maximum diameter out to closer to 1" dia. - this of course effectively makes the taper longer.  I will also extend the Jacobs taper slightly by the same method.

Morse & Jacobs Taper Specifications

(dimensions of the tapered area in contact)

Jacobs Taper   

No.

A

B

C

Taper /ft

Taper /

Taper /

Angle

0

0.2500

0.2284

0.4375

0.5914

0.0493

0.0246

1.4115

1

0.3840

0.3334

0.6563

0.9251

0.0771

0.0385

2.2074

2

0.5590

0.4876

0.8750

0.9787

0.0816

0.0408

2.3351

2 Short

0.5488

0.4876

0.7500

0.9786

0.0815

0.0408

2.3348

3

0.8110

0.7461

1.2188

0.6390

0.0533

0.0266

1.5252

4

1.1240

1.0372

1.6563

0.6289

0.0524

0.0262

1.5010

5

1.4130

1.3161

1.8750

0.6202

0.0517

0.0258

1.4802

6

0.6760

0.6241

1.0000

0.6228

0.0519

0.0260

1.4865

33

0.6240

0.5605

1.0000

0.7620

0.0635

0.0318

1.8185

In Metric* :

No.

A

B

C

Taper mm/25mm

Taper mm/25mm

0

6.350

5.802

11.113

1.232

0.616

1

9.754

8.469

16.669

1.927

0.964

2

14.199

12.386

22.225

2.039

1.019

2 Short

13.940

12.386

19.050

2.039

1.019

3

20.599

18.951

30.956

1.331

0.666

4

28.550

26.345

42.070

1.310

0.655

5

35.890

33.429

47.625

1.292

0.646

6

17.170

15.852

25.400

1.298

0.649

33

15.850

14.237

25.400

1.588

0.794

 

Morse Taper   

Taper

D

P

(P)

A

Taper in/ft

Taper in/in

Taper /

Angle

0

0.2520

2.0000

2.0000

0.3560

0.6240

0.0520

0.0260

1.4894

1

0.3690

2-1/8

2.1250

0.4750

0.5986

0.0499

0.0249

1.4287

2

0.5720

2-9/16

2.5630

0.7000

0.5993

0.0499

0.0250

1.4304

3

0.7780

3-3/16

3.1880

0.9380

0.6023

0.0502

0.0251

1.4375

4

1.0200

4-1/16

4.0630

1.2310

0.6232

0.0519

0.0260

1.4874

5

1.4750

5-3/16

5.1880

1.7480

0.6315

0.0526

0.0263

1.5071

In Metric* :

Taper

D (mm)

P (mm)

A (mm)

Taper mm/25m

1/2 Taper mm/25mm

0

6.401

50.800

9.042

1.300

0.650

1

9.373

53.975

12.065

1.247

0.624

2

14.529

65.100

17.780

1.249

0.624

3

19.761

80.975

23.825

1.255

0.627

4

25.908

103.200

31.267

1.298

0.649

5

37.465

131.775

44.399

1.316

0.658

* (I calculated much of the data for the metric tables above, if you find any errors please let me know - it's your responsibility to double check my metric mm/25mm values - note: Imperial tapers are over 1-inch or 25.4mm, the metric taper is over 25mm).

Taper turning calculations: amount to offset the tailstock (Imperial)