Sieg SC4 Lathe - noise reduction through headstock belt drive conversion

EnglishBreakfast

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Hey everyone!

I wanted to share my experience converting my SIEG SC4 Lathe to a full belt drive system. As I keep my lathe in my apartment, the noise generated from the straight-toothed gears in the headstock was problematic. These gears transfer torque from the intermediary shaft to the main spindle shaft and were loud enough to prevent me from using the optimal spindle rpm for my projects.

Here are some noise level measurements I recorded:

Before the conversion (with Leadscrew Gears disengaged)
  • 80 dB at 500 rpm
  • 87 dB at 1000 rpm
After the conversion (with Leadscrew Gears disengaged)
  • 68 dB at 500 rpm
  • 73 dB at 1000 rpm
  • 77 dB at 1500 rpm
  • 80 dB at the maximum speed of 2000 rpm

Considering that an increase of 10 dB roughly doubles the perceived loudness, this reduction has made a significant difference.

In addition to switching to a belt drive, I upgraded all the bearings to higher-quality SKF ones. This improvement also enhanced the lathe's precision, reducing runout from between 0.02-0.03 mm to just 0.01 mm. GreatOldOne’s post is a goldmine of information for anybody wanting to upgrade the headstock bearings.

I hope this information is of interest or helps anyone thinking about making similar upgrades!

00_A_copy.png

The standard headstock assembly in CAD

00_B.png

The revised assembly with mock-tensioner, timing pulleys and belt

01.jpg

A view inside the headstock… The straight toothed gears had a great deal of backlash and aren’t a great fit on the shafts. The bottom gear can be disengaged via a knob on the control panel. This is because a milling attachment can be used with the lathe and this disengagement stops the main spindle from spinning while carrying out milling operations. As I won’t be using a milling attachment this function isn't necessary.

PXL_20240402_110216185.jpg

Full Parts List for the conversion which came to a total of 95,00 EUR:

• 1x Bearing Spindle Shaft (Front) 32007 X SKF 35x62x18
• 1x Bearing Spindle Shaft (Rear) 6206-2RS1 SKF 30x62x16
• 2x Bearing Intermediary Shaft 61903-2RS1 SKF 17x30x7
• 2x HTD ZRS 30-5M-15 Timing Pulleys (both modified on the lathe to fit the two shafts)
• 1x 265-5M-15 mm Timing Belt (same type of belt as the one between motor/intermediary shaft)
• New Circlips for both shafts
• Bearing Grease

02.jpg

Before disassembling the headstock assembly, I made some modifications to the pulleys. The turning of the final inside diameter was done on another lathe to ensure a good fit as it could be tested with the shafts.

03.jpg

Out with the old…

04.jpg

…and in with the new!

05.jpg

06.jpg

07.jpg

The knob to disengage the gears was removed and the tensioner assembly fitted.

10.jpg

All back together and running much quitter than before! Slight annoyance is to have to run the lathe in "reverse” as now the intermediary and main spindle shaft turn in the same direction rather than opposing as with the toothed gear connection. As a result of this there is also no need for the 2nd 42-tooth-gear for the leadscrew gearbox, as Gear A can be placed directly onto the intermediary spindle shaft instead of the spacer. This insures the power feed runs in the correct direction (towards the headstock) when the lathe is running in "reverse". Didn't worry to much about this as an Electronic Leadscrew Conversion could be next...

A noise comparison video at 1000 rpm:

 
Essentially an AC multiphase motor with a permanent magnet rotor
Brushless AC would be more accurate- I don't know why the DC moniker persists
 
Hey everyone!

I wanted to share my experience converting my SIEG SC4 Lathe to a full belt drive system. As I keep my lathe in my apartment, the noise generated from the straight-toothed gears in the headstock was problematic. These gears transfer torque from the intermediary shaft to the main spindle shaft and were loud enough to prevent me from using the optimal spindle rpm for my projects.

Here are some noise level measurements I recorded:

Before the conversion (with Leadscrew Gears disengaged)
  • 80 dB at 500 rpm
  • 87 dB at 1000 rpm
After the conversion (with Leadscrew Gears disengaged)
  • 68 dB at 500 rpm
  • 73 dB at 1000 rpm
  • 77 dB at 1500 rpm
  • 80 dB at the maximum speed of 2000 rpm

Considering that an increase of 10 dB roughly doubles the perceived loudness, this reduction has made a significant difference.

In addition to switching to a belt drive, I upgraded all the bearings to higher-quality SKF ones. This improvement also enhanced the lathe's precision, reducing runout from between 0.02-0.03 mm to just 0.01 mm. GreatOldOne’s post is a goldmine of information for anybody wanting to upgrade the headstock bearings.

I hope this information is of interest or helps anyone thinking about making similar upgrades!

View attachment 488191
The standard headstock assembly in CAD

View attachment 488181
The revised assembly with mock-tensioner, timing pulleys and belt

View attachment 488182
A view inside the headstock… The straight toothed gears had a great deal of backlash and aren’t a great fit on the shafts. The bottom gear can be disengaged via a knob on the control panel. This is because a milling attachment can be used with the lathe and this disengagement stops the main spindle from spinning while carrying out milling operations. As I won’t be using a milling attachment this function isn't necessary.

View attachment 488184
Full Parts List for the conversion which came to a total of 95,00 EUR:

• 1x Bearing Spindle Shaft (Front) 32007 X SKF 35x62x18
• 1x Bearing Spindle Shaft (Rear) 6206-2RS1 SKF 30x62x16
• 2x Bearing Intermediary Shaft 61903-2RS1 SKF 17x30x7
• 2x HTD ZRS 30-5M-15 Timing Pulleys (both modified on the lathe to fit the two shafts)
• 1x 265-5M-15 mm Timing Belt (same type of belt as the one between motor/intermediary shaft)
• New Circlips for both shafts
• Bearing Grease

View attachment 488183
Before disassembling the headstock assembly, I made some modifications to the pulleys. The turning of the final inside diameter was done on another lathe to ensure a good fit as it could be tested with the shafts.

View attachment 488185
Out with the old…

View attachment 488186
…and in with the new!

View attachment 488187
View attachment 488188
View attachment 488189
The knob to disengage the gears was removed and the tensioner assembly fitted.

View attachment 488190
All back together and running much quitter than before! Slight annoyance is to have to run the lathe in "reverse” as now the intermediary and main spindle shaft turn in the same direction rather than opposing as with the toothed gear connection. As a result of this there is also no need for the 2nd 42-tooth-gear for the leadscrew gearbox, as Gear A can be placed directly onto the intermediary spindle shaft instead of the spacer. This insures the power feed runs in the correct direction (towards the headstock) when the lathe is running in "reverse". Didn't worry to much about this as an Electronic Leadscrew Conversion could be next...

A noise comparison video at 1000 rpm:

Looks great
When buying my mini I did read about the gear noise so got poly-v belt.

I found most will burn the motor at low speed
Right know I am installing a thermometer on my motor .
The motor will burn at 105°C
I would not go over 180°F [85°C]
Thd tape using to attach thr Capillary to motor is HVAC aluminum tape good to 150°C
Thermometer Lathe.jpeg

Dave
Hey everyone!

I wanted to share my experience converting my SIEG SC4 Lathe to a full belt drive system. As I keep my lathe in my apartment, the noise generated from the straight-toothed gears in the headstock was problematic. These gears transfer torque from the intermediary shaft to the main spindle shaft and were loud enough to prevent me from using the optimal spindle rpm for my projects.

Here are some noise level measurements I recorded:

Before the conversion (with Leadscrew Gears disengaged)
  • 80 dB at 500 rpm
  • 87 dB at 1000 rpm
After the conversion (with Leadscrew Gears disengaged)
  • 68 dB at 500 rpm
  • 73 dB at 1000 rpm
  • 77 dB at 1500 rpm
  • 80 dB at the maximum speed of 2000 rpm

Considering that an increase of 10 dB roughly doubles the perceived loudness, this reduction has made a significant difference.

In addition to switching to a belt drive, I upgraded all the bearings to higher-quality SKF ones. This improvement also enhanced the lathe's precision, reducing runout from between 0.02-0.03 mm to just 0.01 mm. GreatOldOne’s post is a goldmine of information for anybody wanting to upgrade the headstock bearings.

I hope this information is of interest or helps anyone thinking about making similar upgrades!

View attachment 488191
The standard headstock assembly in CAD

View attachment 488181
The revised assembly with mock-tensioner, timing pulleys and belt

View attachment 488182
A view inside the headstock… The straight toothed gears had a great deal of backlash and aren’t a great fit on the shafts. The bottom gear can be disengaged via a knob on the control panel. This is because a milling attachment can be used with the lathe and this disengagement stops the main spindle from spinning while carrying out milling operations. As I won’t be using a milling attachment this function isn't necessary.

View attachment 488184
Full Parts List for the conversion which came to a total of 95,00 EUR:

• 1x Bearing Spindle Shaft (Front) 32007 X SKF 35x62x18
• 1x Bearing Spindle Shaft (Rear) 6206-2RS1 SKF 30x62x16
• 2x Bearing Intermediary Shaft 61903-2RS1 SKF 17x30x7
• 2x HTD ZRS 30-5M-15 Timing Pulleys (both modified on the lathe to fit the two shafts)
• 1x 265-5M-15 mm Timing Belt (same type of belt as the one between motor/intermediary shaft)
• New Circlips for both shafts
• Bearing Grease

View attachment 488183
Before disassembling the headstock assembly, I made some modifications to the pulleys. The turning of the final inside diameter was done on another lathe to ensure a good fit as it could be tested with the shafts.

View attachment 488185
Out with the old…

View attachment 488186
…and in with the new!

View attachment 488187
View attachment 488188
View attachment 488189
The knob to disengage the gears was removed and the tensioner assembly fitted.

View attachment 488190
All back together and running much quitter than before! Slight annoyance is to have to run the lathe in "reverse” as now the intermediary and main spindle shaft turn in the same direction rather than opposing as with the toothed gear connection. As a result of this there is also no need for the 2nd 42-tooth-gear for the leadscrew gearbox, as Gear A can be placed directly onto the intermediary spindle shaft instead of the spacer. This insures the power feed runs in the correct direction (towards the headstock) when the lathe is running in "reverse". Didn't worry to much about this as an Electronic Leadscrew Conversion could be next...

A noise comparison video at 1000 rpm:



Thermometer Lathe.jpeg
 
Looks great
When buying my mini I did read about the gear noise so got poly-v belt.

I found most will burn the motor at low speed
Right know I am installing a thermometer on my motor .
The motor will burn at 105°C
I would not go over 180°F [85°C]
Thd tape using to attach thr Capillary to motor is HVAC aluminum tape good to 150°C
View attachment 488344
Dave



View attachment 488344

Hey Dave, I've also been keeping an eye on the temperatures and have noticed that the rear spindle shaft bearing gets hot to the touch rather quickly... Had a more makeshift setup using the temperature read out function of a multimeter to check it. Unfortunately it hasn't improved so far...

Investigating the old bearing (which was practically brand new, < 2hr runtime), I noticed the inner bearing ring has a substantial amount of play... Definitely a lot more than the new SKF one fitted where it wasn't noticeable at all. Because of this I fear the bearing surfaces in the housing could be slightly misaligned leading to extra stresses in the new bearing... Mmmm I guess those are some of the differences between the cheaper chinese lathes and their more expensive counterparts one has to deal with. Currently debating whether to re-use the standard bearing it came with or swapping it for a new self-aligning bearing.
 
Hey Dave, I've also been keeping an eye on the temperatures and have noticed that the rear spindle shaft bearing gets hot to the touch rather quickly... Had a more makeshift setup using the temperature read out function of a multimeter to check it. Unfortunately it hasn't improved so far...

Investigating the old bearing (which was practically brand new, < 2hr runtime), I noticed the inner bearing ring has a substantial amount of play... Definitely a lot more than the new SKF one fitted where it wasn't noticeable at all. Because of this I fear the bearing surfaces in the housing could be slightly misaligned leading to extra stresses in the new bearing... Mmmm I guess those are some of the differences between the cheaper chinese lathes and their more expensive counterparts one has to deal with. Currently debating whether to re-use the standard bearing it came with or swapping it for a new self-aligning bearing.
A high quality ball bearing is best a class 3 or better aka electric motor grade seal for life. They last over 20,000 hours.

The self alignment type is great for manufactured equipment welded together after machining. It avoids line boring.

Dave
 
Hey everyone!

I wanted to share my experience converting my SIEG SC4 Lathe to a full belt drive system. As I keep my lathe in my apartment, the noise generated from the straight-toothed gears in the headstock was problematic. These gears transfer torque from the intermediary shaft to the main spindle shaft and were loud enough to prevent me from using the optimal spindle rpm for my projects.

Here are some noise level measurements I recorded:

Before the conversion (with Leadscrew Gears disengaged)
  • 80 dB at 500 rpm
  • 87 dB at 1000 rpm
After the conversion (with Leadscrew Gears disengaged)
  • 68 dB at 500 rpm
  • 73 dB at 1000 rpm
  • 77 dB at 1500 rpm
  • 80 dB at the maximum speed of 2000 rpm

Considering that an increase of 10 dB roughly doubles the perceived loudness, this reduction has made a significant difference.

In addition to switching to a belt drive, I upgraded all the bearings to higher-quality SKF ones. This improvement also enhanced the lathe's precision, reducing runout from between 0.02-0.03 mm to just 0.01 mm. GreatOldOne’s post is a goldmine of information for anybody wanting to upgrade the headstock bearings.

I hope this information is of interest or helps anyone thinking about making similar upgrades!

View attachment 488191
The standard headstock assembly in CAD

View attachment 488181
The revised assembly with mock-tensioner, timing pulleys and belt

View attachment 488182
A view inside the headstock… The straight toothed gears had a great deal of backlash and aren’t a great fit on the shafts. The bottom gear can be disengaged via a knob on the control panel. This is because a milling attachment can be used with the lathe and this disengagement stops the main spindle from spinning while carrying out milling operations. As I won’t be using a milling attachment this function isn't necessary.

View attachment 488184
Full Parts List for the conversion which came to a total of 95,00 EUR:

• 1x Bearing Spindle Shaft (Front) 32007 X SKF 35x62x18
• 1x Bearing Spindle Shaft (Rear) 6206-2RS1 SKF 30x62x16
• 2x Bearing Intermediary Shaft 61903-2RS1 SKF 17x30x7
• 2x HTD ZRS 30-5M-15 Timing Pulleys (both modified on the lathe to fit the two shafts)
• 1x 265-5M-15 mm Timing Belt (same type of belt as the one between motor/intermediary shaft)
• New Circlips for both shafts
• Bearing Grease

View attachment 488183
Before disassembling the headstock assembly, I made some modifications to the pulleys. The turning of the final inside diameter was done on another lathe to ensure a good fit as it could be tested with the shafts.

View attachment 488185
Out with the old…

View attachment 488186
…and in with the new!

View attachment 488187
View attachment 488188
View attachment 488189
The knob to disengage the gears was removed and the tensioner assembly fitted.

View attachment 488190
All back together and running much quitter than before! Slight annoyance is to have to run the lathe in "reverse” as now the intermediary and main spindle shaft turn in the same direction rather than opposing as with the toothed gear connection. As a result of this there is also no need for the 2nd 42-tooth-gear for the leadscrew gearbox, as Gear A can be placed directly onto the intermediary spindle shaft instead of the spacer. This insures the power feed runs in the correct direction (towards the headstock) when the lathe is running in "reverse". Didn't worry to much about this as an Electronic Leadscrew Conversion could be next...

A noise comparison video at 1000 rpm:

very nice, and that got me to thinking in applications where there is a 2 speed selector switch could a 2nd cogged pully be added to the shafts riding on roller bearings with a dog clutch used to select range?
do you think that a micro v belt would work in this application.
again nice work.
 
Last edited:
Amazing it was that loud, 87db is like an air compressor and not a quiet one.

I assume this conversion also requires a change to an electric lead screw if you want to maintain powerfeed control and threading.
 
very nice, and that got me to thinking in applications where there is a 2 speed selector switch could a 2nd cogged pully be added to the shafts riding on roller bearings with a dog clutch used to select range?
do you think that a micro v belt would work in this application.
again nice work.
yeah that's a cool idea... reminds me of motorcycle gearbox with input and output shaft and shift forks on certain gears to engage and disengage the dog clutch?

I'm not sure how this would work with a belt drive though as the belt would be constantly connected to each of the gears + would run into problems with belt tension if the axial distance was too large (not sure if I've understood the concept completely though :))
 
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