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Country Circular Saw 5.5kW, 350mm Blade, 2900 RPM: Reduce High Rotation & Waving Issue

henryk987 14382 13
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  • #1 16784941
    henryk987
    Level 3  
    Hello, I have a country with 5.5 engine kW three-phase, 2900 revolutions. Pulley on the 130 engine, and on the saw shaft 100. The saw is 350 mm. After starting the saw begins to wave. How to reduce turnover? Change pulleys? I am asking for advice.
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  • Helpful post
    #2 16784969
    fuutro
    Level 43  
    You can buy a special inverter, but it will be drastically cheaper to give another wheel - a larger diameter for a shaft with a saw or a smaller one for a motor shaft. What are the allowable turns for the shield you have?

    When you look around, you have less than 3800 revolutions per minute for the disc rotation, so you have about 400-500 revolutions. Can't see defects on the shield? Is it not rubbing against idle? Is there any beating on the shaft?
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  • #3 16784979
    henryk987
    Level 3  
    Thank you for your answer. Unfortunately, the shield is old and has no inscriptions on it. In that case, how much smaller wheel should be on the motor shaft?
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    #4 16784988
    fuutro
    Level 43  
    There is no one good answer, since the shield is old then try even the same wheel as on the shaft with the shield.
  • #5 16785848
    Anonymous
    Level 1  
  • #6 16787559
    wnoto
    Level 34  
    In my opinion, it makes no sense to combine with pulleys.
    Just replace the shield with a better one.
    We will get the effects:
    - new for relevant (current) turnover
    - sharp teeth (spectral)
    - 3800 revolutions is not a problem for new ones (read descriptions)
    - stiffer

    Prices start from several dozen zlotys.
    What's cut
    Are you sure there is no beat on the shaft?
  • #7 16798912
    qr
    Level 12  
    you checked for a replacement on e-bay
  • #8 16800308
    Anonymous
    Anonymous  
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  • #9 16801432
    fuutro
    Level 43  
    Why are you laughing? The inverter was even used for a small cheap table drill with a tap ;) No sense, except that the threads were cut straight.
  • #10 16816479
    adamzaza
    Level 13  
    With this data from 1 post the saw spins 3770 rpm. turns are ok. Waving the saw may result from damage to the saw (overheating). Check and clean the saw attachment on the shaft.
  • #11 16819309
    robokop
    VIP Meritorious for electroda.pl  
    For an ordinary steel saw for cutting fuel it is too high revs, moreover the saw is prone to scrap if it is prone to scraping, it is overheated (probably just by cutting without a spit or cutting with too high revolutions) - a matter of time when it will break or snatch a fragment from it.
  • #12 17715620
    plazermen
    Level 11  
    Gentlemen, can you treat the inverter as a replacement for different sizes of szajba? For example, I have 35-70 diameter discs and it would suit me not to change the wheels every time. I am mainly interested in whether reducing the speed of the inverter results in an increase in the moment as when changing the ratio or does the moment remain the same?
  • #13 17716281
    Anonymous
    Level 1  
  • #14 17720055
    zimny8
    Level 33  
    A twisted saw can be saved under the press, provided it is worth it.
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Topic summary

✨ The discussion revolves around a 5.5 kW three-phase circular saw with a 350 mm blade that experiences waving issues at startup. Users suggest various solutions, including replacing the pulleys to adjust the RPM, with recommendations for a larger diameter pulley on the saw shaft or a smaller one on the motor shaft. The ideal RPM for a 350 mm saw is noted to be between 2200 to 3550 RPM, and it is advised to check for any defects or beating on the saw shaft. Some participants recommend replacing the old saw blade for better performance, while others discuss the potential use of an inverter to manage speed, although concerns about torque loss are raised. Overall, the consensus leans towards ensuring the saw is in good condition and possibly replacing the blade rather than solely adjusting the pulleys.
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FAQ

TL;DR: With 130:100 pulleys, a 350 mm blade spins about 3770 rpm; “turns are ok,” but wobble signals damage/overheating—clean the mounting. [Elektroda, adamzaza, post #16816479]

Why it matters: Correct speed and a true-running blade prevent dangerous failures and deliver cleaner cuts for DIYers and pros fixing high‑RPM wobble.

Quick Facts

What rpm is my 350 mm blade running with 130:100 pulleys?

With a 2900 rpm motor and 130:100 pulleys, the blade runs about 3770 rpm. That speed is within working limits but near the top end. If you see “waving,” inspect the blade for damage or overheating and clean the mounting faces. [Elektroda, adamzaza, post #16816479]

What rpm range is recommended for a 350 mm circular saw blade?

Typical recommended speed is about 2200–3550 rpm for 350 mm blades. Use clamping discs at least 100 mm in diameter to stiffen the blade and reduce runout. This improves surface finish and reduces heat. “Recommended rotation for a 350 mm saw… 2200 to 3550/min.” [Elektroda, Anonymous, post #16785848]

How can I reduce blade speed without buying a VFD?

Fit same-size pulleys on motor and saw shafts to create a 1:1 ratio. That drops blade speed to near the motor’s 2900 rpm, landing inside the recommended range for many 350 mm blades. Check flange diameter and mounting while you’re there. [Elektroda, Anonymous, post #16785848]

Will a VFD replace pulley swaps and boost torque at lower rpm?

A VFD can reduce speed, but torque will be the same or lower. Power decreases proportionally with rpm, and motor cooling worsens at low speeds. Use pulley reduction when you need more torque at the blade. [Elektroda, Anonymous, post #17716281]

Why does the blade “wave” right after start-up?

Waving often means the blade is damaged or overheated. Clean the arbor, flanges, and blade bore, then retest. If waving persists, the blade is likely distorted and should be replaced. “Waving… may result from damage… check and clean the saw attachment.” [Elektroda, adamzaza, post #16816479]

Is high rpm dangerous for ordinary steel ‘fuel’ saw blades?

Yes. For ordinary steel blades used for fuel wood, excessive rpm accelerates heating and can cause cracking. An overheated, scraping blade becomes brittle; fragments may break off under load. Reduce rpm or replace the blade to avoid failure. [Elektroda, robokop, post #16819309]

Should I just replace an old, unmarked blade?

Yes. New blades specify allowable rpm, have sharp teeth, and are stiffer. Many quality 350 mm blades are rated around 3800 rpm; always verify the label. Replacement is often cheaper than chasing pulleys first. [Elektroda, wnoto, post #16787559]

How do I quickly diagnose wobble or runout?

  1. Measure axial runout on the clamping disc with a dial indicator.
  2. If runout is high, fix or replace the disc and recheck.
  3. Test with a known-good blade; if true, leave speed alone and keep the new disc. “Measure the axial runout… buy a new disc.” [Elektroda, 3034452, post #16800308]

Do equal pulleys really help with wobble and noise?

Equal pulleys reduce speed and stress, which can calm borderline blades. Try the same wheel size on motor and saw shafts as a low-cost test before buying electronics. This also simplifies future belt replacements. [Elektroda, fuutro, post #16784988]

What clamping disc (flange) size should I use?

Use flanges at least 100 mm in diameter for a 350 mm blade. Larger, flat, clean flanges reduce runout and help prevent blade flutter. Undersized or dirty flanges cause wobble and poor cut quality. [Elektroda, Anonymous, post #16785848]

Can a bent or twisted blade be straightened?

Sometimes. A skilled shop can straighten a twisted blade under a press. This only makes sense for valuable blades; otherwise, replace it to restore safety and cut accuracy quickly. [Elektroda, zimny8, post #17720055]

Is 3800 rpm acceptable for modern 350 mm blades?

Many new blades list ratings around 3800 rpm. Always follow the printed specification on your blade. Upgrading improves stiffness and tooth quality, which helps at higher speeds. “3800 revolutions is not a problem for new ones.” [Elektroda, wnoto, post #16787559]

Could the shaft or arbor be the source of the problem?

Yes. Check for shaft beat (runout), burrs, or contamination. Even a slight arbor defect can induce wobble at speed and ruin cut quality. Fixing the shaft issue and fitting a new blade often solves it. [Elektroda, wnoto, post #16787559]

Does changing pulleys cost less than adding an inverter?

Yes. Swapping to a larger saw-shaft pulley or smaller motor pulley is a low-cost way to lower rpm. Many users choose equal pulleys to hit the motor’s base speed without electronics. [Elektroda, fuutro, post #16784969]

I switch between 35–70 mm discs; will a VFD save me pulley swaps?

A VFD lets you dial rpm for different accessories, but it does not increase torque at low speed. If heavy cuts bog the motor, use pulley reduction to gain mechanical advantage. [Elektroda, Anonymous, post #17716281]
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