REF: Tools - 147


Types of Reamers

  • Reaming: 1)
    • The process of cutting a larger hole (to a precise measurement).
    • The purpose is to not only make the hole the correct diameter but also to align it and square it with the part that goes into it.
    • This usually means line reaming (aligning it with a hole, or bearing, opposite and at the other end of a shaft).
  • Line Reaming: 2)
    • Line reaming is the process of using additional support features to help provide shaft alignment. In this case of reaming cam bushings, it is the cam cover and its associated bushing that is used to “line up” the reaming tool so that the bushing hole in the right crankcase is cut to the correct size diameter, is properly located horizontally, and is cut square to the intended shaft axis.

L to R:

  1. Jig bore reamer.
  2. Chucking reamer. (this reamer has a chamfered which is a good choice for blind holes and typically used in a machining chuck)
  3. Bridge reamer. *this reamer has a lead in taper)
  4. Hand reamer (this reamer has a lead in taper just like the bridge type although the taper is much shallower)
  5. Tapered reamer.
  6. Shell reamer. (fits on an arbor)
1 thru 5 3)6. Shell Reamer 4)
A reamer cuts along its chamfer angle,
not on its outside diameter. 5)
Bridge and Hand Reamers have a starting taper that
is too long for blind hole work. Each has a different
starting taper angle. 6)

Rocker Arm Bushing Reamer (94804-57)

See also Rocker Arm Bushing Replacement in the Sportsterpedia.

This reamer is specially designed for reaming the rocker arm bushings from 1957 to present.
It is the right length and cut to fit into the old bushing on one end of the rocker arm and ream the new bushing in the other end.

“Jims” makes this reamer referenced to HD part number (94804-57) 7)

Calculating Pre-Ream Drill Hole Sizes

The amount of material left in the hole prior to reaming (pre-ream hole size) plays an integral role in the quality of the reamed hole. 8)
The pre-ream hole size affects characteristics in the reamed hole including hole finish, hole straightness, tool life, and cycle time.
There are several ways in which the pre-ream hole size may be obtained some examples include investment casting, boring, line boring, rough reaming, and stamping.
The most common way to obtain the pre-ream hole size is through drilling.
The appropriate amount of stock removal for carbide tipped and solid carbide reamers is generally 2% to 3% of the finished hole size.
Carbide tipped and solid carbide reamers need to have adequate stock to remove or they will rub in the hole and generate excessive heat.
This leads to premature tool wear and poor hole finishes. A 0.7500” diameter reamer should remove between 0.0150”-0.0225” of stock.
A 0.2500” diameter reamer should remove between 0.0050”-0.0075” of stock.

A good way to calculate the drill bit size is to take the desired finished hole diameter and multiply it by 0.98
Then take the desired finished hole size and multiply it by 0.97
This gives you the range of stock removal best suited to the finish ream hole size.
From that range refer to a standard drill chart to chose the appropriate standard drill size for your pre reamed hole size.
Below are examples for calculating the pre-ream drill hole size for a 0.7500” finished hole diameter and a 0.2500” finished hole diameter.

0.7500“ x 0.98 = 0.7350”0.7500“ x 0.97 = 0.7275”

Therefore, the appropriate range of the pre-ream drill hole size for a 0.7500” finished hole;
0.7275” – 0.7350”

0.2500“ x 0.98 = 0.2450”0.2500“ x 0.97 = 0.2425”

Therefore, the appropriate range of the pre-ream drill hole size for a 0.2500” finished hole;
0.2425” – 0.2450”

If you are fine tuning your operation and are within the 2%-3% range;
Try removing 2% of the reamer diameter for steels and tough alloys..
And 3% for non-ferrous and cast iron materials..
If you are rough reaming, stock removal can be up to 5% of the reamer diameter.

The 2%-3% rule is great in theory.
In the real world drill bits come in standard sizes.
Most do not have time or money to wait for a special size drill bit to be made.
You are usually forced to choose among standard drill bit sizes that are on the shelf.
A Pre-Ream Drill Hole Size Chart is provided below.
The chart tells the appropriate standard drill bit size to choose when reaming fractional diameters from 1/8” to 1” in 1/64” increments.

Pre-Ream Drill Hole Size Chart

A PDF of this chart can be downloaded from Rock River Tool Inc. 9)

Reamer diameter
fraction - decimal (nom)
Hole size
to leave 2%
Drill size
to leave 2%
Hole size
to leave 3%
Drill size
to leave 3%
1/8“ - .1250”.1225“31.1213”3.0mm
9/64“ - .1406”.1378“29.1364”3.4mm
5/32“ - .1562”.1532“24.1516”25
11/64“ - .1719”.1685“19.1667”4.2mm
3/16“ - .1875”.1838“14.1819”15
13/64“ - .2031”.1990“5.0mm.1970”9
7/32“ - .2188”.2144“5.4mm.2122”4
5/64“ - .2344”.2297“1.2274”5.7mm
1/4“ - .2500”.2450“C.2425”6.1mm
17/64“ - .2656”.2600“6.5mm.2576”F
9/32“ - .2812”.2756“I.2728”6.9mm
19/64“ - .2969”.2910“7.3mm.2880”7.25mm
5/16“ - .3125”.3063“7.75mm.3031”N
21/64“ - .3281”.3215“8.1mm.3183”O
11/32“ - .3438”.3370“8.5mm.3335”8.4mm
23/64“ - .3594”.3522“S.3486”8.8mm
3/8“ - .3750”.3675“9.25mm.3638”23/64
25/64“ - .3906”.3828“9.6mm.3789”V
13/32“ - .4062”.3982“10.0mm.3941”25/64
27/64“ - .4219”.4135“10.4mm.4092”13/32
7/16“ - .4375”.4288“10.8mm.4244”27/64
29/64“ - .4531”.4440“11.2mm.4395”7/16
15/32“ - .4688”.4594“11.6mm.4547”29/64
31/64“ - .4844”.4747“12.0mm.4699”15/32
1/2“ - .5000”.4900“31/64.4850”12.2mm
33/64“ - .5156”.5053“1/2.5000”12.6mm
17/32“ - .5312”.5206“33/64.5153”13.0mm
35/64“ - .5469”.5360“17/32.5305”13.4mm
9/16“ - .5625”.5513“35/64.5456”13.8mm
37/64“ - .5781”.5665“9/16.5608”14.2mm
19/32“ - .5938”.5820“37/64.5760”14.5mm
39/64“ - .6094”.5972“19/32.5911”14.9mm
5/8“ - .6250”.6125“39/64.6063”15.3mm
41/64“ - .6406”.6278“5/8.6214”15.7mm
21/32“ - .6562”.6431“41/64.6365”16.1mm
43/64“ - .6719”.6585“21/32.6517”16.5mm
11/16“ - .6875”.6738“17.0mm.6669”16.8mm
45/64“ - .7031”.6890“11/16.6820”17.2mm
23/32“ - .7188”.7044“45/64.6972”17.6mm
47/64“ - .7344”.7197“18.2mm.7124”18.0mm
3/4“ - .7500”.7350“18.5mm.7275”18.3mm
49/64“ - .7656”.7502“18.9mm.7426”18.8mm
25/32“ - .7812”.7656“19.3mm.7578”3/4
51/64“ - .7969”.7810“19.7mm.7730”49/64
13/16“ - .8125”.7963“20.1mm.7881”25/32
53/64“ - .8281”.8115“20.5mm.8034”51/64
27/32“ - .8438”.8270“20.8mm.8185”13/16
55/64“ - .8594”.8422“21.25mm.8336”53/64
7/8“ - .8750”.8575“21.6mm.8488”27/32
57/64“ - .8906”.8728“22.0mm.8639”55/64
29/32“ - .9062”.8881“22.5mm.8790”7/8
59/64“ - .9219”.9035“22.8mm.8942”57/64
15/16“ - .9375”.9188“23.25mm.9094”29/32
61/64“ - .9531”.9340“23.5mm.9245”59/64
31/32“ - .9688”.9494“24.0mm.9397”15/16
63/64“ - .9844”.9647“24.4mm.9549”61/64
1“ - 1.0000”.9800“24.75mm.9700”31/32

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