RC Tank Warfare community hobby forum

Hello,
hello, wishing to install bearings on the Sherman tensioner rollers (Tamiya), I am looking for a solution, to enlarge the hole from 5 to 8 mm, without risking to break everything? thank you in advance for your advice

I think the title has your answer. You need a pedestal drill or milling machine with the correct sized bit. I've recently done this sort of task on a number of Trumpeter wheels using a pedestal drill. Only real tip is to ensure everything is fixed firmly, the parts are correctly aligned and you maybe drill the hole in two size steps. Check twice, cut once!

I have a universal tool bench £30ish on E-Bay bolted to a pedestal drill base with a machine vise bolted to it,
I had a problem with a pair of metal PZ4 Gearbox output covers, They fitted the Metal hull just fine but internally there was no space for the output shaft bearings,
The external irregular shape of the covers were a challenge, My solution was to line the inner jaws of the vise with sponge and that holds the cover securely,
Put a milling cutter into the drill and then lowered the cutter into the cover then using the for and aft and left and right handles of the bench I cut the inside to size.
That was with Metal, Plastic could provide a challenge.

Can we see a picture of the item, with the hole you need to enlarge.

Thank you, indeed by successively drilling different diameters, maybe less risk of breakage? that's what scares me a little, especially if the forest has teeth? I think it is preferable to proceed at low speed with a strawberry system, lest the plastic heat up and it will jam again, thank you for your advice.
Can we see a picture of the item, with the hole you need to enlarge.

You could use a step drill bit if you haven't got a pillar drill.
One like on the link below. If you were to use the 4 to 8mm drill bit, you could put a short length of 5mm tube with a 4mm bore on the smaller 4mm section.
It would help guide the 8mm drill bit.
Sadly the bits below are for wood, and may be overly fierce with their cut.

Drillpro 4-8/5-9/6-10mm Twist Step Drill Bit For Woodworking Manual Pocket Hole Drill Sale | UK Mobile - Banggood Mobile
https://uk-m.banggood.com/Drillpro-4-8- ... YvEALw_wcB

I have used stepped drill bits with great success. Even if the stepped bit doesn't go all the way through you can switch to a straight bit after getting the pilot hole drilled with the stepped bit. Being here in 'Merica had to special order a Metric stepped bit set as they can't be found at most stores.

Thank you very much for your responses and your help.

Have you considered drilling 0.5mm extra and using brass tubing as a bearing sleeve? Or will the 8mm allow you to press a bearing inside?

Good idea but there may be less play if you press fit straight into the plastic but l advise you use flanged bearings to assure correct alignment and precise fit. I got that tip from Tankme and it works.