- Joined
- Jul 1, 2022
- Messages
- 8
Bottom line: A four-step pulley was scavenged off of an old drill press, and so I need to determine a replacement. (That, and I need to actually find one in stock and for sale.)
This posting describes how I guesstimated what four-step pulley I need to return an old 12-speed drill press to service. In essence, one of three four-step pulleys was missing. The manufacturer is long gone, service manual, diagrams, parts specs aren't available. So a bit of arithmetic was used to calculate the minimum changes in the vbelts' lengths, based on the two remaining pulleys and the specs on commercially available pulleys.
OK, so I've been gifted an Orbit Machine Tools OR-1458 drill press. My eldest brother picked it up at auction in the 1990's, and pretty much forgot about it till I asked about it. The issue I'm dealing with at the moment is, the 4-step pulley for the motor spindle is missing. In its place was a bent / wobbly single-groove 3.25" sheet metal thing and a couple loose-fitting vbelts. I've replaced this with a like cast iron pulley and tight vbelts. So I've now got a working single speed thing, but with RPMs only suitable for woodworking.
The calculations --
The outside diameters of the two existing pulleys were measured, recorded in a spreadsheet. The vbelt lengths for each of the grooves were calculated as 1/2 of the OD circumferences of the first pulley plus 1/2 of the OD circumferences of the second pulley, plus two times the distance between their centers. The second pulley is on a swing, able to adjust about 1" in either direction. I just set it in the middle, used that for measurements.
The same arithmetic was used to estimate the vbelt lengths between the second pulley and third pulley replacement options. Basically, pasting in the four diameters for commercially vended four-step pulleys identified a unit that'd: 1) minimize the change in vbelt lengths (i.e., tension) and, 2) a useful range of 12 speeds.
What'd I determine? Per Mr. Google, there are two suitable four-step pulleys --
McMaster-Carr 6213K55: 1-3/4, 2-1/4, 2-3/4, 3-1/4
Chicago Die Casting 1416: 1-1/32, 1-19/32, 2-11/32, 2-28/32
Availability? Well, OK. Any help would be welcome. I tried to order a McMaster-Carr 6213K55; they cancelled the order about 20 minutes later, saying it's not in stock and might not be for a year or three. The Chicago pulley I can find on eBay, but comments re: quality control for Chicago's last years of production are a worry. That, and I've found _wildly_ different sets of dimensions for their #1416. I found a decades-old Chicago catalog; it did not list this unit; no certainty on the actual dimensions.
[Other issues --
1. The wiring to the motor was a mess, with a weird junction box hanging by the wires from the motor, swinging in the air; easily fixed. But, this and the scavenged pulley indicates poor maintenance at least and maybe abuse.
2. The motor might not be original. Placard suggests it's off of an HVAC fan. The shaft is not long enough for a four-step pulley, given that the set screws all seem to be in the second-smallest groove. If it were the second largest, the short shaft wouldn't be an issue.
3. The drill spindle makes a noticeable noise when running. Cadence seems to be at the same rate as the RPMs. The head still makes the noise with the unbent pulley on t he motor spindle. Hopefully, greasing the spindle bearings will resolve this.
4. I need to get at the drill head's bearings, re-grease. I'm presuming it's two ball races.
5. Rust on the table from sitting mostly unused in a barn since the 1990's was resolved by a 45 minute dip in oxalic acid.
6. A bit of trig will give me a new speeds chart [once I've got a four-step pulley].]
This posting describes how I guesstimated what four-step pulley I need to return an old 12-speed drill press to service. In essence, one of three four-step pulleys was missing. The manufacturer is long gone, service manual, diagrams, parts specs aren't available. So a bit of arithmetic was used to calculate the minimum changes in the vbelts' lengths, based on the two remaining pulleys and the specs on commercially available pulleys.
OK, so I've been gifted an Orbit Machine Tools OR-1458 drill press. My eldest brother picked it up at auction in the 1990's, and pretty much forgot about it till I asked about it. The issue I'm dealing with at the moment is, the 4-step pulley for the motor spindle is missing. In its place was a bent / wobbly single-groove 3.25" sheet metal thing and a couple loose-fitting vbelts. I've replaced this with a like cast iron pulley and tight vbelts. So I've now got a working single speed thing, but with RPMs only suitable for woodworking.
The calculations --
The outside diameters of the two existing pulleys were measured, recorded in a spreadsheet. The vbelt lengths for each of the grooves were calculated as 1/2 of the OD circumferences of the first pulley plus 1/2 of the OD circumferences of the second pulley, plus two times the distance between their centers. The second pulley is on a swing, able to adjust about 1" in either direction. I just set it in the middle, used that for measurements.
The same arithmetic was used to estimate the vbelt lengths between the second pulley and third pulley replacement options. Basically, pasting in the four diameters for commercially vended four-step pulleys identified a unit that'd: 1) minimize the change in vbelt lengths (i.e., tension) and, 2) a useful range of 12 speeds.
What'd I determine? Per Mr. Google, there are two suitable four-step pulleys --
McMaster-Carr 6213K55: 1-3/4, 2-1/4, 2-3/4, 3-1/4
Chicago Die Casting 1416: 1-1/32, 1-19/32, 2-11/32, 2-28/32
Availability? Well, OK. Any help would be welcome. I tried to order a McMaster-Carr 6213K55; they cancelled the order about 20 minutes later, saying it's not in stock and might not be for a year or three. The Chicago pulley I can find on eBay, but comments re: quality control for Chicago's last years of production are a worry. That, and I've found _wildly_ different sets of dimensions for their #1416. I found a decades-old Chicago catalog; it did not list this unit; no certainty on the actual dimensions.
[Other issues --
1. The wiring to the motor was a mess, with a weird junction box hanging by the wires from the motor, swinging in the air; easily fixed. But, this and the scavenged pulley indicates poor maintenance at least and maybe abuse.
2. The motor might not be original. Placard suggests it's off of an HVAC fan. The shaft is not long enough for a four-step pulley, given that the set screws all seem to be in the second-smallest groove. If it were the second largest, the short shaft wouldn't be an issue.
3. The drill spindle makes a noticeable noise when running. Cadence seems to be at the same rate as the RPMs. The head still makes the noise with the unbent pulley on t he motor spindle. Hopefully, greasing the spindle bearings will resolve this.
4. I need to get at the drill head's bearings, re-grease. I'm presuming it's two ball races.
5. Rust on the table from sitting mostly unused in a barn since the 1990's was resolved by a 45 minute dip in oxalic acid.
6. A bit of trig will give me a new speeds chart [once I've got a four-step pulley].]
